Electrical Unit Converter — W, kW, hp, BTU, kVA & A
Every nameplate on a job site uses a different unit. Motors give horsepower, heaters give watts, HVAC equipment gives BTU per hour or tons, transformers and generators give kVA, and the code tables want amps. This converter moves between all of them — including the current conversions that need voltage and power factor to be meaningful.
Convert electrical units
Used in power-unit mode only.
Supply details
Required to convert between power and current.
Converted to watts
Using 1 hp = 745.7 W and 1 W = 3.412142 BTU/h.
Motor branch circuits must be sized from the NEC Table 430.248 and 430.250 full-load currents, not from a horsepower conversion. Cooling tonnage is heat moved, not electrical input.
The conversions, explained in plain English
Horsepower is output, not input
A 1 hp motor delivers 745.7 W at the shaft but draws more than that from the supply, because efficiency is never 100%. Divide by efficiency to get input power.
Cooling tons aren't watts
A ton is 12,000 BTU/h of heat moved. A heat pump moving 3,517 W of heat might draw only 1,000 W to do it — which is the whole point of a heat pump.
Worked examples
A motor nameplate, an HVAC crossover, and a generator comparison.
1 horsepower motor
The defaults above.
= 745.7 × 3.412142 = 2,544 BTU/h
= 0.212 tons of refrigeration equivalent
Result: 745.7 W is shaft output. At 85% efficiency the motor draws about 877 W from the supply, and its branch circuit would still be sized from NEC Table 430.248 rather than either figure.
5 kW electric heater in BTU
Crossing from the electrical to the HVAC side of a job.
at 240 V single-phase, PF 1.0: 5,000 ÷ 240 = 20.83 A → 30 A circuit
Result: electric resistance heat converts one-for-one, so 5 kW is exactly 17,061 BTU/h. This is how you compare a strip-heat kit against a gas furnace rating — and note the 20.83 A it draws, which is what pushes electrification onto larger services.
A "100 kVA" generator
Published at the industry-standard 0.8 power factor.
at 480 V three-phase: 100,000 ÷ (1.732 × 480) = 120.3 A
Result: comparing an 85 kW calculated load against a "100 kVA" generator looks fine but is actually over capacity — the machine only makes 80 kW. Always compare kVA to kVA.
Conversion constants
The figures behind every conversion on this page, rendered from the same constants the calculator uses.
| From | Equals | Note |
|---|---|---|
| 1 horsepower | 745.7 W | Electrical hp, used in NEC motor tables |
| 1 kilowatt | 1.341 hp | Roughly 1⅓ hp |
| 1 watt | 3.412142 BTU/h | The electrical-to-thermal bridge |
| 1 kilowatt | 3,412 BTU/h | |
| 1 horsepower | 2,544 BTU/h | |
| 1 ton of refrigeration | 12,000 BTU/h | 3,517 W of heat moved |
| 1 kVA at PF 1.0 | 1,000 W | Apparent equals real only at unity |
| 1 kVA at PF 0.8 | 800 W | Typical generator rating basis |
Sources & standards: electrical horsepower = 745.7 W; 1 W = 3.412142 BTU/h; 1 ton of refrigeration = 12,000 BTU/h. NEC (NFPA 70) 2023 — 430.6(A)(1) and Tables 430.248 and 430.250 require motor conductors to be sized from tabulated full-load currents rather than from nameplate horsepower. Generator kVA ratings are conventionally published at 0.8 power factor.
Frequently asked questions
Common questions about electrical power units and what they actually mean.
How many watts is 1 horsepower?
745.7 watts for electrical horsepower — the value used throughout NEC motor calculations. You will also see 746 W used as a round figure, and metric horsepower (PS) at 735.5 W, but 745.7 is the one to work from on US electrical jobs. Note this is output power: a motor rated 1 hp draws more than 745.7 W of input because of its efficiency.
How do I convert watts to BTU per hour?
Multiply by 3.412142. So 1,000 W = 3,412 BTU/h, and 1 hp = 2,544 BTU/h. Going the other way, divide BTU/h by 3.412142. This conversion is how you cross between the electrical and HVAC sides of a job — a 5,000 W electric heater and a 17,061 BTU/h heater are the same appliance.
How many watts is a ton of cooling?
One ton of refrigeration is 12,000 BTU/h, which is 3,517 W of heat removed. That is not the electrical input — a modern 1-ton air conditioner might draw only 900 to 1,200 W to move 3,517 W of heat, because it pumps heat rather than generating it. Never size a circuit from cooling tonnage; use the equipment nameplate.
Why don't watts and volt-amperes match?
They match only at unity power factor. Volt-amperes is voltage times current — the load the conductor carries. Watts is the portion doing real work. A 1,000 VA load at 0.8 power factor delivers 800 W. Conductors, breakers, transformers, and generators are all rated in VA. The kVA Calculator covers the relationship properly.
Can I size a motor circuit from its horsepower?
Not directly from a horsepower-to-watts conversion. NEC 430.6(A)(1) requires motor branch-circuit conductors to be sized from the full-load current tables — 430.248 for single-phase and 430.250 for three-phase — rather than from the nameplate or from a calculation. Those table values are deliberately higher than the arithmetic suggests. Use this converter for estimating and cross-checking, not for the final circuit design.
What's the difference between kW and kVA on a generator?
The kW rating is what the engine can deliver as real power; the kVA rating is what the alternator can carry as apparent power. Standby generators are commonly published at 0.8 power factor, so a 100 kVA unit is an 80 kW unit. When you compare a calculated load against a generator, compare kVA to kVA — comparing your kW to its kVA will oversell the machine by 25%.
Units sorted? Quote the job in seconds.
Nameplate decoded, load known — now price it. Describe the job or upload photos and TradesQuote's AI builds a detailed line-item estimate with quantities, unit prices, and totals, validated by a built-in quality control agent.
AI line-item estimates
Quantities, unit prices, and totals generated instantly.
Knowledge base
Upload past jobs so estimates reflect your real pricing.
Shareable & signable
Clients review, accept, and sign from a public link.
No credit card required · 14-day free trial · Cancel anytime