BTU Unit Converter
Convert BTU to watts, kilowatts, calories, joules, therms, tons of refrigeration, and horsepower instantly.
Room Details
Room Size vs BTU Reference
| Room Area | BTU/hr | Tonnage |
|---|---|---|
| 100 sq ft | 2,500 | 0.21 |
| 150 sq ft | 3,750 | 0.31 |
| 200 sq ft | 5,000 | 0.42 |
| 300 sq ft | 7,500 | 0.63 |
| 400 sq ft | 10,000 | 0.83 |
| 500 sq ft | 12,500 | 1.04 |
| 700 sq ft | 17,500 | 1.46 |
| 1,000 sq ft | 25,000 | 2.08 |
| 1,500 sq ft | 37,500 | 3.13 |
| 2,000 sq ft | 50,000 | 4.17 |
Based on standard 8 ft ceiling, moderate climate, and average insulation. Adjust 20–35% upward for tropical climates or poor insulation.
Room & Temperature Details
Room Dimensions
Commercial Space Details
Convert BTU
BTU
12.0000k
BTU (British Thermal Unit)
W
3.5169k
Watts
kW
3.516853
Kilowatts
cal
3.0260M
Calories (thermochemical)
J
12.6607M
Joules
thm
0.120000
Therms
TR
0.999996
Tons of Refrigeration
hp
4.716180
Horsepower (mechanical)
Power Units Comparison
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BTU Unit Conversion Reference
| Unit | Per 1 BTU |
|---|---|
| BTU (British Thermal Unit) (BTU) | 1.000000 |
| Watts (W) | 0.293071 |
| Kilowatts (kW) | 2.9307e-4 |
| Calories (thermochemical) (cal) | 252.164000 |
| Joules (J) | 1,055.060000 |
| Therms (thm) | 1.0000e-5 |
| Tons of Refrigeration (TR) | 8.3333e-5 |
| Horsepower (mechanical) (hp) | 3.9301e-4 |
What Is the BTU Unit Converter?
The BTU Unit Converter translates energy and power values between BTU (British Thermal Unit), watts, kilowatts, calories, joules, therms, tons of refrigeration, and horsepower. Enter any value in any of these eight units and see all equivalents simultaneously — useful when comparing American (BTU/hr) and European (kW) HVAC equipment, sizing electrical service, or interpreting utility bills.
How It Works
Reference Constants
1 BTU = 1,055.06 joules = 252.164 cal = 0.29307 watt-hours. The converter holds these constants to seven significant figures, matching NIST reference data.
BTU/hr vs BTU
BTU is energy; BTU/hr is power. The converter treats values as BTU/hr (power) by default since that's how HVAC equipment is rated. Multiply by run hours for total energy.
Tons of Refrigeration
1 TR = 12,000 BTU/hr exactly. This historical unit comes from melting one ton of ice in 24 hours, absorbing 286,000 BTU in the process.
Therms for Gas
1 therm = 100,000 BTU. Natural gas is metered in therms (or kBTU in some regions). A typical US home uses 500–1,000 therms per winter.
6 Ways to Use This Calculator
Compare US and EU Equipment
US heat pump rated at 36,000 BTU/hr → European spec sheet shows 10.55 kW. The converter makes shopping-spec parity instant.
Read a Gas Bill
Your utility bill shows therms used. Convert to BTU to compare with the input rating on your furnace and estimate efficiency.
Size Electrical Service
Convert AC BTU to watts to estimate panel current draw — divide watts by SEER and by voltage to get amps.
Interpret Boiler Ratings
Old boilers are rated in BTU input; modern boilers in kW output. Convert between them to compare efficiency apples-to-apples.
Quote Engine Cooling
Internal-combustion engines reject heat at roughly 1 hp ≈ 2,545 BTU/hr. Sizing a radiator? Convert hp to BTU directly.
Engineering Coursework
Thermodynamics problems hop between SI and US customary units. The converter sidesteps the manual factor lookups every textbook requires.
Best Practices
Always be explicit about energy vs power. BTU alone is energy (joules); BTU/hr is power (watts). Confusing the two is the most common mistake — a 12,000 BTU/hr AC is not equivalent to 12,000 BTU of energy in any meaningful way. When in doubt, work in SI: joules and watts are unambiguous.
For utility bills, divide your therms by your fuel cost ($/therm) for a clean operating cost figure. For HVAC equipment comparisons, the kW figure on the European spec sheet is the equivalent of BTU/hr — never the kW on a refrigeration nameplate, which is electrical input, not cooling output.
Why It Matters
Cross the Unit Boundary
Globalised supply chains mean a single project might mix US-spec ductwork and European-spec heads. The converter is the bridge.
Translate Cooling to Electrical
Sizing breaker panels, generators, or UPS systems for HVAC loads requires moving from BTU to watts — and dividing by COP to get true draw.
Compare Apples to Apples
Specifications from different manufacturers, regions, and eras use different units. The converter normalizes everything.
Avoid Costly Conversion Errors
A single missing factor of 12,000 between BTU/hr and tons has caused real-world sizing disasters. The converter eliminates the math at risk.
Common Energy & Power Equivalents
| Range | Category | Meaning | Recommendation |
|---|---|---|---|
| 1 BTU | Reference | Energy to raise 1 lb of water by 1°F. | = 1,055.06 J = 252.164 cal = 0.29307 Wh |
| 1 BTU/hr | HVAC Power | Standard US HVAC rating unit. | = 0.29307 W = 0.0000833 ton refrigeration |
| 12,000 BTU/hr | 1 Ton AC | Smallest typical residential ducted unit. | = 3.517 kW cooling capacity |
| 100,000 BTU | 1 Therm | Natural gas billing unit. | ≈ 100 ft³ of natural gas at standard conditions |
| 2,545 BTU/hr | 1 Mechanical HP | Engine/motor heat rejection benchmark. | = 745.7 W = 0.7457 kW |
Core Formulas
Energy Equivalents
1 BTU = 1,055.06 J = 252.164 cal
NIST reference values for the International Table BTU. The thermochemical BTU differs by ~0.0001 — negligible for HVAC.
Power Equivalents
1 BTU/hr = 0.29307 W ; 1 ton = 12,000 BTU/hr = 3.517 kW
Use these to convert between US (BTU/hr, tons) and SI (W, kW) HVAC capacity ratings.
Gas and Mechanical
1 therm = 100,000 BTU ; 1 hp = 2,545 BTU/hr
Therm is used for natural gas billing; horsepower bridges to mechanical and engine specifications.
Common Mistakes to Avoid
- 1
Confusing BTU (energy) with BTU/hr (power) — they describe different physical quantities.
- 2
Using SEER as a conversion factor — SEER is a ratio of cooling to electrical input, not a unit conversion.
- 3
Forgetting that European cooling kW = output (matches BTU/hr); electrical kW = input (drawn from outlet).
- 4
Mixing food calories (kcal) and thermochemical calories — they differ by 1,000×.
- 5
Converting horsepower as if all hp are equal — boiler horsepower (33,475 BTU/hr) is very different from mechanical horsepower (2,545 BTU/hr).
About Our Methodology
Calculations follow the ASHRAE Handbook of Fundamentals and ACCA Manual J / N simplified load methods. Conversion constants are NIST reference values. Results are a planning starting point — for projects above 5 tons or any commercial, healthcare, restaurant, or server-room work, engage a licensed mechanical engineer. Read our editorial policy.
Frequently Asked Questions
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