Quick power conversion reference
Common equivalences—use the calculator above for exact factors and every unit.
| 1 horsepower (mechanical) | 745.7 W |
|---|---|
| 1 horsepower (metric / PS) | 735.5 W |
| 1 kW | 1,000 W ≈ 1.341 hp (mechanical) |
| 1 ton of refrigeration | 12,000 Btu/h ≈ 3.517 kW |
| 1 Btu/h (IT) | 0.293 W |
| 1 J/s | 1 W |
What is power?
Power is the rate at which energy is transferred or converted: energy per unit time. The SI unit is the watt (W): 1 W = 1 J/s (one joule per second). Multiples such as kW and MW are standard when sizing electrical loads, breakers, and utility demand—for circuit relationships among voltage, current, and resistance, an Ohm’s Law calculator is a useful companion. Horsepower appears in automotive and machinery specs (mechanical, metric, and electrical definitions differ slightly); shaft power in rotating equipment is often discussed alongside torque (N·m or lbf·ft). Btu/h, MBH (thousands of Btu/h), and ton of refrigeration (≈ 12 000 Btu/h) are standard in HVAC and heat flux work when you move from total equipment capacity to power per unit area. Calorie per hour or second ties thermal chemistry to power. For steady DC or unity power factor AC, volt-ampere (VA) equals watts; in general, VA is apparent power.
This converter keeps a clear line between power (W, Btu/h, hp) and energy (J, kWh, Btu as an amount). Multiply power by time to get energy—for example, 1 kW for 1 hour is 1 kWh of energy.
How power conversion works
Each unit is stored as its exact equivalent in watts. To convert, multiply your value by the source unit’s watt factor, then divide by the target unit’s watt factor:
Example: 1 hp (mechanical, UK/US) ≈ 745.7 W, so 2 hp ≈ 1491 W. Another: 1 Btu (IT)/h ≈ 0.293 W, so 12 000 Btu/h (one ton of refrigeration) ≈ 3.52 kW.
Key power units explained
Short reference for the units people search most often.
Watt [W]
SI base for this tool
1 W = 1 J/s. Named after James Watt. Used for electrical, mechanical, and thermal power rates.
Kilowatt [kW]
1 kW = 1000 W
Motor ratings, solar inverters, and household loads are often quoted in kW.
Horsepower [hp]
Mechanical (550 ft·lbf/s) ≈ 745.7 W
Metric hp (PS) ≈ 735.5 W. Boiler, electric, and water hp definitions differ—this converter lists each.
Btu (IT)/hour
≈ 0.293071 W per Btu/h
US heating and cooling capacity. MBH is 1000 Btu/h. Ton of refrigeration ≈ 12 000 Btu/h.
Volt-ampere [V·A]
1 V·A = 1 W (for this converter’s factor)
Apparent power for AC; equals watts at unity power factor. kV·A is common for transformer and UPS ratings.
Joule per second [J/s]
1 J/s = 1 W
Same dimension as watt; prefixed forms (kJ/s, MJ/s, …) match the corresponding watt prefixes.
Power vs energy (don’t mix them up)
Power answers “how fast?”—joules per second, Btu per hour, or shaft hp. Energy answers “how much total?”—joules, kWh, or Btu as a quantity. A 2 kW heater running 3 hours uses 6 kWh of energy; its power while on is 2 kW. Use this page for rates; use an energy converter for amounts.
Who uses a power converter?
HVAC engineers and technicians convert Btu/h, MBH, and tons of refrigeration to kW for loads and electrical sizing—often alongside heat flux density when normalizing by floor or coil area. Automotive and industrial teams compare hp, kW, and PS for mechanical output. Electrical designers relate W, kW, and kV·A. Students check homework (J/s to W, erg/s to W, etc.). All calculations run locally in your browser.
Btu (IT) vs Btu (th)
Btu (IT) uses the international steam-table calorie; Btu (th) uses the thermochemical calorie. The difference per Btu is small but measurable when you chain many conversions. Equipment specs in the US usually imply Btu (IT) unless labeled otherwise. This tool includes both rate forms (per hour, minute, second) for IT and th.
Common power conversions at a glance
Handy reference; use the calculator above for exact values.
| From | To | Relationship | Example |
|---|---|---|---|
| kW | W | × 1000 | 5 kW = 5000 W |
| hp (mechanical) | kW | × 0.7457 | 100 hp ≈ 74.57 kW |
| Btu (IT)/h | W | × 0.293071 | 12 000 Btu/h ≈ 3.52 kW |
| MBH | kW | × 0.293071 | 10 MBH ≈ 2.93 kW |
| J/s | W | 1:1 | 2500 J/s = 2500 W |
Avoiding common mistakes
Do not treat Btu/h as an energy unit—it is already a rate. Do not assume every horsepower is the same: pick mechanical, metric, electric, boiler, or water to match your datasheet. For AC, VA and W diverge when power factor is not 1. When in doubt, convert everything to watts here, then apply your system’s assumptions.
Power Conversion FAQ
? How many watts are in one horsepower?
Mechanical horsepower (550 ft·lbf/s) is 745.699871582 W in this tool. Metric horsepower (PS) is 735.49875 W. Electric horsepower is often taken as 746 W. Choose the matching unit in the dropdown.
? How do I convert Btu/h to kW?
Multiply Btu (IT)/h by 0.29307107 to get kilowatts (approximately). For example, 18 000 Btu/h ≈ 5.28 kW. Use the converter above for exact factors including Btu (th).
? What is a ton of refrigeration?
One US ton of refrigeration is a cooling rate of about 12 000 Btu (IT)/h, or roughly 3.517 kW. It is a power unit, not a mass.
? Is a watt the same as a joule per second?
Yes: 1 W = 1 J/s by definition. The same numeric prefixes apply (e.g. kJ/s = kW).
? Are volt-amperes the same as watts?
For DC or AC with power factor 1, VA equals watts. For general AC, apparent power (VA) can exceed real power (W); use W for heat and billing, VA for wire and transformer sizing.
? What is MBH?
MBH means thousands of Btu per hour (M = 1000 in Roman numerals in this context). 1 MBH ≈ 1000 Btu (IT)/h ≈ 0.293 kW.