How to Convert Watts to BTU (and BTU/hr to Watts)
Learn how to convert watts to BTU per hour, reverse BTU/hr to watts, and avoid common mistakes when estimating air conditioner power use. This guide includes detailed conversion tables, real-world HVAC examples, electric heater calculations, and UDPOWER portable power station sizing and runtime estimates.
Quick answer: To convert watts to BTU per hour, multiply watts by 3.412142. To convert BTU per hour to watts, multiply by 0.293071, or divide by 3.412142.
1 watt = 3.412142 BTU/hr
1 BTU/hr = 0.293071 watt
A 1,500W electric space heater is therefore equivalent to about 5,118 BTU/hr of heat. However, a 12,000 BTU/hr air conditioner does not normally draw 3,517 electrical watts. That number is its thermal-power equivalent. Actual AC input depends on efficiency and is better estimated with watts = BTU/hr ÷ EER.
Quick Watts-to-BTU Reference
Use the formulas below for a direct power conversion. The values are based on the International Table BTU conversion used in the NIST conversion tables.
BTU/hr = watts × 3.412142
Watts = BTU/hr × 0.293071
Watts = BTU/hr ÷ 3.412142
| Starting Value | Calculation | Converted Value | Typical Use |
|---|---|---|---|
| 500W | 500 × 3.412142 | 1,706 BTU/hr | Small heating load or appliance heat output |
| 1,000W | 1,000 × 3.412142 | 3,412 BTU/hr | General electrical-to-thermal comparison |
| 1,500W | 1,500 × 3.412142 | 5,118 BTU/hr | Common electric space-heater setting |
| 5,000 BTU/hr | 5,000 × 0.293071 | 1,465 thermal watts | Thermal equivalent only; not necessarily AC input |
| 12,000 BTU/hr | 12,000 × 0.293071 | 3,517 thermal watts | Thermal equivalent only; use EER for AC input |
Air-conditioner warning: Converting BTU/hr directly to watts gives a thermal-power equivalent, not the air conditioner's actual electrical draw. For an air conditioner, use the EER method later in this guide or check the unit's nameplate watts.
Watts and BTU Conversion Formulas
Watts to BTU per hour
BTU/hr = watts × 3.412141633
For everyday calculations, multiplying by 3.412 is usually precise enough.
BTU per hour to watts
Watts = BTU/hr × 0.29307107
Watts = BTU/hr ÷ 3.412141633
Kilowatts to BTU per hour
BTU/hr = kilowatts × 3,412.142
For example, 2.4kW equals about 8,189 BTU/hr of thermal power.
BTU to watt-hours
Watt-hours = total BTU × 0.293071
This formula is for a total amount of energy, not a per-hour rating. For example, 10,000 BTU of total energy equals about 2,931Wh.
The Three Numbers People Often Confuse
Most bad watts-to-BTU advice comes from answering the wrong question. Before calculating, decide whether you need thermal equivalence, actual electrical draw, or battery runtime.
| What you are trying to find | Best formula | Example | What the answer means |
|---|---|---|---|
| Thermal equivalent of electrical power | Watts × 3.412142 | 1,500W = 5,118 BTU/hr | Useful for electric resistance heaters, electronics heat load, and direct unit conversion. |
| Electrical draw of an air conditioner | BTU/hr ÷ EER | 12,000 BTU/hr ÷ EER 12 = 1,000W | Approximate compressor-and-fan input while the AC is operating at its rated condition. |
| Estimated power-station runtime | Battery Wh × 0.90 ÷ actual load W | 2,083Wh × 0.90 ÷ 1,000W = 1.87 hours | A planning estimate that includes a 10% allowance for conversion losses. |
The practical rule: Use BTU/hr to understand heating or cooling capacity. Use actual input watts and startup surge to decide whether a portable power station can run the appliance. Use watt-hours to estimate how long it will run.
Watts to BTU/hr Conversion Table
The table below converts electrical or thermal power in watts to its BTU-per-hour equivalent. Values are rounded for easy planning.
| Watts | BTU/hr | Common interpretation | Conversion source |
|---|---|---|---|
| 1W | 3.41 BTU/hr | Base conversion | NIST |
| 50W | 171 BTU/hr | Small heated pad or electronics heat load | NIST factor |
| 100W | 341 BTU/hr | Heated blanket or small equipment load | NIST factor |
| 200W | 682 BTU/hr | Low-watt personal heater | NIST factor |
| 300W | 1,024 BTU/hr | Compact personal heating | NIST factor |
| 400W | 1,365 BTU/hr | Small personal heater or equipment heat output | NIST factor |
| 500W | 1,706 BTU/hr | Low heater setting | NIST factor |
| 600W | 2,047 BTU/hr | Compact heater or combined electronics load | NIST factor |
| 750W | 2,559 BTU/hr | Half-power setting on many space heaters | NIST factor |
| 800W | 2,730 BTU/hr | Medium heating load | NIST factor |
| 1,000W | 3,412 BTU/hr | 1kW of heat output | NIST factor |
| 1,200W | 4,095 BTU/hr | High electrical load or medium heater | NIST factor |
| 1,500W | 5,118 BTU/hr | Typical full-power portable space heater | NIST factor |
| 1,800W | 6,142 BTU/hr | High-load heating or appliance input | NIST factor |
| 2,000W | 6,824 BTU/hr | 2kW thermal power | NIST factor |
| 2,400W | 8,189 BTU/hr | 2.4kW thermal power | NIST factor |
| 3,000W | 10,236 BTU/hr | 3kW thermal power | NIST factor |
| 5,000W | 17,061 BTU/hr | Large resistive heating load | NIST factor |
| 10,000W | 34,121 BTU/hr | 10kW thermal power | NIST factor |
BTU/hr to Watts Conversion Table
This is a direct thermal-power conversion. Do not automatically treat the result as an air conditioner's electrical consumption.
| BTU/hr | Thermal watts | Thermal kilowatts | Useful interpretation |
|---|---|---|---|
| 500 | 146.5W | 0.147kW | Small heat-transfer rate |
| 1,000 | 293.1W | 0.293kW | About 293 thermal watts |
| 2,000 | 586.1W | 0.586kW | About 0.59kW thermal |
| 3,000 | 879.2W | 0.879kW | About 0.88kW thermal |
| 4,000 | 1,172.3W | 1.172kW | About 1.17kW thermal |
| 5,000 | 1,465.4W | 1.465kW | Common small room-AC capacity |
| 6,000 | 1,758.4W | 1.758kW | Cooling-capacity equivalent |
| 8,000 | 2,344.6W | 2.345kW | Cooling-capacity equivalent |
| 10,000 | 2,930.7W | 2.931kW | Cooling-capacity equivalent |
| 12,000 | 3,516.9W | 3.517kW | One ton of cooling capacity |
| 14,000 | 4,103.0W | 4.103kW | Larger room-AC capacity |
| 18,000 | 5,275.3W | 5.275kW | 1.5 tons of cooling capacity |
| 24,000 | 7,033.7W | 7.034kW | Two tons of cooling capacity |
| 36,000 | 10,550.6W | 10.551kW | Three tons of cooling capacity |
How Many Watts Does a BTU-Rated Air Conditioner Use?
An air conditioner's BTU rating describes how much heat it can remove from a room per hour. It is not the same as the electricity the unit consumes. The direct conversion of 12,000 BTU/hr to 3,517W tells you the cooling capacity in equivalent thermal watts, not the plug load.
For a room air conditioner, the better estimate is:
Estimated running watts = cooling capacity in BTU/hr ÷ EER
The U.S. Department of Energy defines EER as the ratio of cooling capacity in BTU/hr to electrical input in watts. A higher EER means the unit provides more cooling for each watt consumed. See the Department of Energy EER definition.
| AC cooling capacity | Approx. watts at EER 8 | Approx. watts at EER 10 | Approx. watts at EER 12 | Approx. watts at EER 14 |
|---|---|---|---|---|
| 5,000 BTU/hr | 625W | 500W | 417W | 357W |
| 6,000 BTU/hr | 750W | 600W | 500W | 429W |
| 8,000 BTU/hr | 1,000W | 800W | 667W | 571W |
| 10,000 BTU/hr | 1,250W | 1,000W | 833W | 714W |
| 12,000 BTU/hr | 1,500W | 1,200W | 1,000W | 857W |
| 14,000 BTU/hr | 1,750W | 1,400W | 1,167W | 1,000W |
| 18,000 BTU/hr | 2,250W | 1,800W | 1,500W | 1,286W |
| 24,000 BTU/hr | 3,000W | 2,400W | 2,000W | 1,714W |
Example: A 10,000 BTU/hr window AC with an EER of 12 is estimated at about 833W while operating. A different 10,000 BTU/hr model with an EER of 8 may draw about 1,250W. The same BTU rating can therefore require a very different power station.
Use the nameplate before the estimate
The most reliable number is the input wattage printed on the appliance label or listed by the manufacturer. If watts are not shown, check voltage and amperage, then use watts = volts × amps as a conservative estimate. The full method is explained in the UDPOWER guide to volts-to-watts conversion.
Do not use SEER as if it were running EER
SEER and SEER2 are seasonal ratings. They help compare efficiency over a cooling season, but they are not ideal for estimating the immediate plug load that a portable power station must support. For backup-power planning, prioritize the appliance's rated input watts, running amps, EER, and startup information.
Startup surge still matters
Air conditioners use compressors and fans. The running wattage may fit within a power station's continuous rating while the compressor startup spike causes an overload. Check the AC manual for startup current, locked-rotor amps, soft-start compatibility, or measured peak watts. Leave practical headroom rather than choosing a power station whose rating exactly matches the estimated running load.
For a deeper appliance-specific walkthrough, see How Many Watts Does a Window AC Use? and Can a Solar Generator Power an AC?.
BTU size is not the only room-sizing factor
The Department of Energy uses about 20 BTU per square foot as a starting point for room air conditioners, then recommends adjusting for ceiling height, sunlight, occupancy, kitchens, and room layout. An oversized AC may cool quickly but remove humidity poorly. Review the DOE room air-conditioner sizing guidance before buying a unit solely from a square-foot estimate.
Heaters, Heat Pumps, and Furnaces: The Conversion Changes by Equipment Type
Electric resistance heaters
For a plug-in space heater, baseboard heater, heating element, or electric kettle, nearly all electrical input eventually becomes heat in the space. The direct watts-to-BTU/hr conversion is therefore a useful approximation.
| Heater setting | Approx. heat output | Battery demand | Practical takeaway |
|---|---|---|---|
| 200W | 682 BTU/hr | Low | Personal warming, but limited room-heating effect |
| 500W | 1,706 BTU/hr | Moderate | Better for close-range comfort than whole-room heating |
| 750W | 2,559 BTU/hr | High for a battery | Often the low setting on a standard space heater |
| 1,000W | 3,412 BTU/hr | Very high for extended battery use | Short-duration heating unless the battery is large |
| 1,500W | 5,118 BTU/hr | Extremely high for extended battery use | Common full-power setting; drains portable batteries quickly |
A heater can be compatible with a power station and still have disappointing runtime. The guide How Long Can a Portable Power Station Run a Heater? compares low-watt heaters, heated blankets, and 1,500W space heaters.
Heat pumps
A heat pump moves heat instead of producing all of it through electrical resistance. Its delivered heat can be several times its electrical input. Use the coefficient of performance, or COP:
Heating output in BTU/hr ≈ input watts × COP × 3.412142
Example: A heat pump drawing 1,000W at a COP of 3 delivers about 3,000 thermal watts, or roughly 10,236 BTU/hr. COP changes with outdoor temperature, operating speed, defrost cycles, and equipment condition, so the nameplate and manufacturer performance data still matter.
Gas and oil furnaces
Do not divide a furnace's 60,000 or 80,000 BTU/hr heating rating by 3.412 and assume that is its electrical demand. Most of that heat comes from fuel. A backup battery normally powers the blower motor, controls, igniter, and related accessories. For power-station sizing, use the furnace's electrical nameplate watts or amps and check motor startup demand.
Using BTU and Watts to Choose a Portable Power Station
After converting the appliance information, use this four-step process.
1. Find actual running watts
Use the appliance nameplate first. For AC equipment, use BTU/hr ÷ EER only when actual input watts are unavailable. For a resistance heater, its watt setting is normally the relevant running load.
2. Check startup watts
Compressors, pumps, and blower motors may need a short burst of extra power. Compare that demand with the power station's surge capability. A surge rating is not permission to run a higher continuous load indefinitely.
3. Add every device that will run at the same time
If the AC draws 800W, a refrigerator averages 100W while running, and lights use 40W, the combined operating load is about 940W before allowing for startup spikes and changing duty cycles.
4. Estimate runtime from watt-hours
Estimated runtime = battery capacity in Wh × 0.90 ÷ actual appliance watts
The 90% factor is a practical UDPOWER planning estimate for inverter and conversion losses. Real runtime changes with ambient temperature, battery state, inverter overhead, appliance cycling, and startup behavior.
| Constant AC load | C600 596Wh / 600W |
S1200 1,190Wh / 1,200W |
S2400 2,083Wh / 2,400W |
Typical interpretation |
|---|---|---|---|---|
| 400W | About 1.34 hr | About 2.68 hr | About 4.69 hr | Small efficient AC, dehumidifier, or low heater setting |
| 500W | About 1.07 hr | About 2.14 hr | About 3.75 hr | Efficient 5,000–6,000 BTU room AC in some cases |
| 600W | About 0.89 hr | About 1.79 hr | About 3.12 hr | C600 is at its continuous-output ceiling |
| 800W | Not within 600W continuous rating | About 1.34 hr | About 2.34 hr | Common efficient 8,000–10,000 BTU AC range |
| 1,000W | Not compatible as a continuous load | About 1.07 hr | About 1.87 hr | Efficient 10,000–12,000 BTU AC or heavy appliance |
| 1,200W | Not compatible as a continuous load | About 0.89 hr | About 1.56 hr | S1200 is at its continuous-output ceiling |
| 1,500W | Not compatible as a continuous load | Above the 1,200W continuous rating | About 1.25 hr | Typical space heater on high |
| 2,000W | Not compatible as a continuous load | Not compatible as a continuous load | About 0.94 hr | High-draw appliance; confirm surge and plug requirements |
Why an AC may run longer than the table: The table assumes the listed wattage stays constant. Once a room cools, a single-speed compressor may cycle off, and an inverter AC may reduce output. In severe heat, poor insulation, direct sun, or an undersized room, the compressor may run almost continuously, bringing actual runtime closer to the constant-load estimate.
Recommended UDPOWER Models for Cooling, Heating, and BTU-Rated Appliances
Choose from the appliance's actual electrical input, not from BTU capacity alone. The product recommendations below use official UDPOWER specifications and a 90% runtime-planning factor.
UDPOWER C600: Best for Efficient Loads Under 600W
- Battery capacity: 596Wh LiFePO4
- Continuous AC output: 600W pure sine wave
- Maximum / surge output: up to 1,200W
- Weight: 12.3 lb
- AC outlets: 2
The C600 is the portable option for low-watt cooling equipment, fans, dehumidifiers, and selected efficient 5,000–6,000 BTU room AC units whose measured running input stays below 600W. Compressor startup must also remain within the unit's limits.
At a constant 500W load, the 90% estimate is about 1.07 hours. Appliance cycling may extend real runtime, but a hot room can keep an AC operating continuously.
View UDPOWER C600
UDPOWER S1200: Best Balanced Choice for Loads Up to 1,200W
- Battery capacity: 1,190Wh LiFePO4
- Continuous AC output: 1,200W pure sine wave
- Startup surge support: up to 1,800W
- Weight: 26.0 lb
- Outputs: 5 AC outlets plus 10 DC outputs on the 5-AC version
The S1200 is a practical match for selected window ACs, portable ACs, dehumidifiers, and other appliances whose real input stays at or below 1,200W and whose startup surge is compatible. It is not the right continuous-power match for a standard 1,500W space heater on high.
Estimated constant-load runtime is about 1.34 hours at 800W, 1.07 hours at 1,000W, or 0.89 hour at 1,200W.
View UDPOWER S1200
UDPOWER S2400: Best for High-Watt Cooling and Short-Duration Electric Heat
- Battery capacity: 2,083Wh LiFePO4
- Continuous AC output: 2,400W pure sine wave
- Startup surge support: up to 3,000W
- Weight: 40.8 lb
- Outputs: 6 AC outlets plus 10 DC outputs
The S2400 provides the most headroom for larger 120V portable or window AC units, multiple essential loads, and high-watt appliances. It can support a typical 1,500W space heater within its continuous-output rating, but battery runtime is still only about 1.25 hours at a constant 1,500W load.
For cooling, the estimate is about 2.34 hours at 800W, 1.87 hours at 1,000W, and 1.56 hours at 1,200W before considering compressor cycling.
View UDPOWER S2400Compatibility check before buying: Find the appliance's running watts, startup watts or amps, voltage, plug type, and whether it requires a dedicated circuit. The power station must meet all of those requirements. A BTU rating by itself is not enough.
Common Watts-to-BTU Mistakes
Calling BTU and BTU/hr the same thing
BTU is energy. BTU/hr is power. Watts convert directly to BTU/hr, while watt-hours convert to total BTU.
Assuming 12,000 BTU/hr means 3,517 electrical watts
That is the thermal equivalent. A 12,000 BTU/hr AC may draw around 857W at EER 14, 1,000W at EER 12, 1,200W at EER 10, or 1,500W at EER 8.
Choosing a battery from watts alone
Watts determine whether the appliance can run. Watt-hours determine runtime. A 2,400W inverter can support a 1,500W heater, but the finite battery capacity still limits use to a relatively short period.
Ignoring compressor or motor startup
An AC, dehumidifier, refrigerator, or furnace blower may briefly demand much more than its normal running watts. Check startup information and leave headroom.
Using a marketing BTU number instead of the appliance label
Portable AC listings may show more than one BTU rating under different test standards. Use the exact model's nameplate input, manufacturer specification sheet, and U.S. rating information rather than a generic product-family number.
Assuming every heater is a good battery load
Resistance heating consumes stored energy quickly. For overnight outage comfort, a heated blanket, heated mattress pad, layered insulation, or localized low-watt heat usually lasts much longer than a 1,500W room heater.
Worked Examples
Example 1: Convert a 1,500W heater to BTU/hr
1,500 × 3.412142 = 5,118 BTU/hr
A standard 1,500W electric space heater produces roughly 5,118 BTU/hr of heat. On the S2400, the constant-load planning estimate is about 1.25 hours.
Example 2: Estimate a 5,000 BTU window AC at EER 12
5,000 ÷ 12 = 417W estimated running input
This may fit the C600's 600W continuous rating, but only after confirming the actual nameplate watts and compressor startup demand. At a constant 417W load, the 90% battery estimate is about 1.29 hours on C600.
Example 3: Estimate a 12,000 BTU portable AC at EER 10
12,000 ÷ 10 = 1,200W estimated running input
This reaches the S1200's continuous rating, leaving little room for other devices or startup variation. The S2400 provides more operating headroom. Estimated constant-load runtime is about 0.89 hour on S1200 or 1.56 hours on S2400.
Example 4: Estimate heat-pump output from 900W input and COP 3.2
900 × 3.2 × 3.412142 = 9,827 BTU/hr
The heat pump can deliver roughly 9,827 BTU/hr under those operating conditions while drawing about 900W. Outdoor temperature and defrost operation can lower real performance.
Frequently Asked Questions
How many BTU per hour is 1 watt?
One watt equals approximately 3.412142 BTU per hour.
How many watts is 1 BTU per hour?
One BTU per hour equals approximately 0.293071 watt.
How many BTU is a 1,500W heater?
A 1,500W electric resistance heater is equivalent to about 5,118 BTU/hr.
How many BTU is 1,000 watts?
One thousand watts equals about 3,412 BTU/hr.
How many watts does a 5,000 BTU air conditioner use?
It depends on efficiency. At EER 10, the estimate is 500W. At EER 12, it is about 417W. Confirm the actual model's nameplate watts and startup demand.
How many watts does a 12,000 BTU air conditioner use?
At EER 10, the estimate is 1,200W. At EER 12, it is 1,000W. At EER 14, it is about 857W. Real draw varies by model and operating conditions.
Is 12,000 BTU the same as 3,517 electrical watts?
No. The 3,517W figure is the direct thermal equivalent of 12,000 BTU/hr. An air conditioner's electrical input is lower because EER measures how much cooling it provides per watt.
Can I use SEER to calculate an AC's running watts?
SEER is a seasonal efficiency rating, so it is not the best number for immediate generator or power-station sizing. Use nameplate watts, rated amps, EER, and startup information instead.
Can a 1,200W power station run a 12,000 BTU AC?
Sometimes, but not from the BTU rating alone. The AC's actual running input must stay within 1,200W, and its compressor startup demand must also be compatible. A unit estimated at exactly 1,200W leaves almost no headroom.
Can the UDPOWER S2400 run a 1,500W space heater?
Its 2,400W continuous AC rating can support a 1,500W heater, but estimated runtime is only about 1.25 hours at a constant 1,500W load using a 90% planning factor.
What is the difference between watts and watt-hours?
Watts measure power at a moment in time. Watt-hours measure stored or consumed energy over time. Output watts determine whether an appliance can run; battery watt-hours help determine runtime.
What is the difference between BTU and BTU/hr?
BTU is a quantity of energy. BTU/hr is a rate of heat transfer. Watts convert directly to BTU/hr, not to BTU without a time period.
Calculation and Specification Sources
Choose a Power Station from Actual Appliance Watts
Start with the appliance nameplate, confirm startup demand, then choose enough battery capacity for the runtime you need.
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