Power Converter (W, kW, MW)

Understanding the power converter — concept and principle

This converter changes a power value between watts, kilowatts, megawatts, gigawatts, BTU per hour and kilocalories per hour. Use it to compare appliance ratings, heater and air-conditioner capacities, generator sizes or power-plant outputs that are quoted in different units.

How it is calculated

Every unit is first converted to watts, then divided by the size of the target unit:

result = value × (watts per "from" unit) ÷ (watts per "to" unit)

• 1 kW = 1,000 W, 1 MW = 10⁶ W, 1 GW = 10⁹ W.
• 1 BTU/h = 0.2930710702 W (International Table BTU).
• 1 kcal/h (IT) = 1.163 W.

The table under the result shows the same value in every other unit.

The principle

Power is the rate of energy transfer: 1 watt is 1 joule per second. A unit of power is therefore always "energy unit ÷ time unit". The BTU/h comes from the British thermal unit (1,055.05585262 J) divided by 3,600 seconds, and kcal/h from the IT kilocalorie (4,186.8 J) divided by 3,600 s, which is exactly 1.163 W. Because all the factors are fixed definitions, the conversion is exact apart from display rounding.

Worked example

Default inputs: 1 kilowatt to watts.

1. Convert to the base unit: 1 kW × 1,000 = 1,000 W.
2. Divide by the size of the target unit (1 W): 1,000 ÷ 1 = 1,000 W.
3. The same 1 kW is 0.001 MW, 0.000001 GW, 1,000 ÷ 0.2930710702 = 3,412.141633 BTU/h and 1,000 ÷ 1.163 = 859.8452279 kcal/h.

How to read the result

For a feel of scale: a phone charger draws a few to tens of watts, a hair dryer or kettle around 1–2 kW, a household air conditioner a few kW of cooling, and a large power-plant unit around 1 GW. Air-conditioner and heater capacity is often quoted in BTU/h or kcal/h; cooling capacity is heat removed, not electricity consumed. To find electricity use, divide cooling capacity by the efficiency ratio (COP or EER) given by the maker.

Common mistakes

• Confusing kW (power) with kWh (energy). A 2 kW heater running 3 hours uses 6 kWh.
• Mixing cooling capacity with electrical input power.
• Using an old thermochemical calorie (4.184 J) or a different BTU definition; the factors differ slightly.
• Reading "MW" (megawatt) as "mW" (milliwatt).

Frequently asked questions

How many BTU/h is 1 kW?

About 3,412.14 BTU/h.

How many watts is 1 BTU/h?

0.2930710702 W.

What is the difference between kW and kWh?

kW is the rate of using energy; kWh is the amount used. Multiply kW by hours to get kWh.

How do I convert kcal/h to kW?

Multiply by 1.163 and divide by 1,000. For example, 3,000 kcal/h is about 3.49 kW.

Sources: BIPM, The International System of Units (SI Brochure), 9th edition · NIST Special Publication 811 (2008), Appendix B