Universal Power & Energy Unit Converter
Electrical, mechanical, and thermal systems each tend to favor different units by convention — watts and kilowatts in general electrical work, horsepower in mechanical/automotive contexts, BTU/hour in HVAC, and joules in physics and scientific contexts. This page is a single reference point for converting between all of them, rather than needing a separate calculator for each specific pair.
Power Unit Conversion Reference
| From → To | Multiply By |
|---|---|
| Watts → Kilowatts | ÷ 1,000 |
| Kilowatts → Watts | × 1,000 |
| Kilowatts → Megawatts | ÷ 1,000 |
| Horsepower (mechanical) → kW | × 0.7457 |
| kW → Horsepower (mechanical) | ÷ 0.7457 |
| BTU/hour → Watts | × 0.2931 |
| Watts → BTU/hour | × 3.4121 |
| kW → BTU/hour | × 3,412.14 |
| VA (apparent power) → W (at PF=1) | × 1 (equal if PF=1) |
Energy Unit Conversion Reference
| From → To | Multiply By |
|---|---|
| kWh → Joules | × 3,600,000 |
| kWh → Megajoules | × 3.6 |
| kWh → BTU | × 3,412.14 |
| kWh → Watt-hours | × 1,000 |
| Watt-hours → kWh | ÷ 1,000 |
| kWh → Megawatt-hours | ÷ 1,000 |
| BTU → kWh | ÷ 3,412.14 |
| Joules → kWh | ÷ 3,600,000 |
Why So Many Units Exist for the Same Underlying Concepts
It comes down to which industry standardized first, and around what measurement tools were available. Electrical engineering in most of the world settled on watts (from SI units, honoring James Watt) for power and kilowatt-hours for billed energy, because that maps directly onto how electricity meters work. Mechanical engineering and the automotive industry, especially in markets with a strong historical tie to steam-engine-era measurement, kept horsepower. HVAC in North America inherited BTU from an older imperial thermal measurement tradition. None of these were designed to be mutually compatible — they each solved a specific industry's measurement problem independently, which is exactly why conversion tools like this one stay useful long after any of these units were first defined.
A Worked Multi-Unit Example
A 15 hp motor, running for 3 hours, and you want the answer in both kWh and BTU:
Frequently Asked
Which unit should I use for my own project?
Match whatever unit your source documentation, equipment nameplate, or utility bill uses — converting everything into kWh is usually the most broadly useful common ground, since that's what most billing and most cross-comparisons (solar output, appliance costs, generator sizing) are ultimately measured against.
Is kVA the same category as kW here?
Not exactly — kVA (apparent power) needs a power factor to convert accurately to kW (real power); see the kVA to kW calculator for that specific conversion, since it isn't a fixed multiplier the way the unit pairs above are.
Why isn't horsepower exactly a round number in kW?
Because horsepower was originally defined empirically (based on estimates of a horse's sustained work output in the 18th century), not derived mathematically from the metric system — so its conversion factor to kW is a measured constant (0.7457) rather than a clean round number.
For the specific calculators behind each of these conversions, use the main kW to kWh calculator, horsepower to kW calculator, or BTU to kWh calculator.
Founder & Lead Renewable Energy Specialist
Abdul Rehman is a Renewable Energy Consultant and Solar Systems Specialist. He built kwtokwh.com to provide transparent, accessible calculation tools that help homeowners, electricians, and facility engineers accurately convert electrical power (kW) into billed energy consumption (kWh) calibrated against NIST and IEC metrology standards.