BTU to kWh Calculator

How to use the BTU to kWh calculator

Enter an energy figure in BTU and this tool returns the same energy in kilowatt-hours — the unit your electricity meter counts. It is the reverse of the kwh-to-btu-calculator: instead of taking kilowatt-hours you already know and expressing them as British thermal units, you start from a BTU figure and convert it back to kWh. One number in, one number out, and no dollars anywhere, because this is a straight unit conversion rather than a cost estimate. The input is pre-filled with 10,000 BTU so you can see the conversion before swapping in your own figure, and because the factor is a definition rather than a measurement, the result carries no uncertainty beyond the rounding on the display.

A BTU is a unit of energy — historically the heat needed to raise one pound of water by one degree Fahrenheit, and today fixed at exactly 1,055.05585262 joules — and a kilowatt-hour is also a unit of energy, so converting between them is just changing the scale, the way you would convert miles to kilometres. Because both sides measure the same thing, the conversion factor is fixed and universal: it never depends on a price, a provider, a season, or where you live. That is what makes this tool clean. It answers how many kWh a given amount of energy is, and then it stops, leaving the money question to a tool that asks for your rate.

Here is the nuance that trips people up, and it is worth getting right before you use the number for anything. On an air conditioner, the BTU printed on the box is almost always a cooling-output rate — BTU per hour of heat the unit can move — not the electricity it draws. A 10,000 BTU per hour air conditioner does not consume 2.93 kWh of electricity for every hour it runs. It draws far less, because its efficiency rating means it shifts several BTU of heat for each BTU of electrical energy it uses. At an illustrative EER of 12 BTU per watt-hour, that same 10,000 BTU per hour unit pulls about 833 watts, or 0.83 kWh an hour, which is well under a third of the naive answer.

Use this tool when the BTU is genuinely an energy quantity: the heat content of a fuel, a heating load someone has quoted you in BTU, or any total BTU figure you want stated in kWh. One therm of natural gas is 100,000 BTU and therefore 29.31 kWh of raw energy; a gallon of propane at the heat content EIA publishes, 91,452 BTU, is 26.80 kWh; a gallon of distillate heating oil at 137,381 BTU is 40.26 kWh. Those are the comparisons this conversion was built for. When you do want a running cost in dollars rather than energy, take the real electrical figure into the electricity-cost-calculator, which multiplies kWh by your own rate.

The formula

Both BTU and kilowatt-hours measure energy, so converting from one to the other is a single division by a fixed factor. One kilowatt-hour equals 3,412.14 BTU, so dividing a BTU figure by 3,412.14 gives the same energy in kWh. There is nothing to estimate and nothing personal to enter, because the relationship between the two units is settled by definition rather than by measurement.

The definition runs like this: a kilowatt-hour is one kilowatt held for one hour, which is 3,600,000 joules, and the international-table BTU used throughout energy statistics is fixed at 1,055.05585262 joules. Divide the first by the second and 3,412.14 falls out. The US Energy Information Administration publishes the same factor rounded to 3,412, so a small disagreement between an official conversion table and this tool is rounding rather than a different physical claim.

kWh = BTU ÷ 3412.14
BTU = kWh × 3412.14   (the reverse)
therms = BTU ÷ 100,000
electrical watts of an AC = cooling BTU per hour ÷ EER

Worked example with the default: 10,000 ÷ 3,412.14 = 2.9307 kWh, shown as 2.93. The factor works in both directions and scales without correction, so 3,412.14 BTU is precisely 1.00 kWh, 5,000 BTU comes to 1.47 kWh, and 100,000 BTU — one therm — is 29.31 kWh. Halve the BTU and the kWh halves with it. Nothing in the result depends on a price or a provider, which is why two people in different states converting the same BTU figure get the same answer to the last decimal.

Now the air conditioner caveat, worked through properly, because it is where this conversion is most often misread. The BTU on an air conditioner box is a cooling-output rate: heat moved per hour, not electricity consumed. A 10,000 BTU per hour unit does not use 2.93 kWh of electricity each hour. Its electrical draw is the cooling rating divided by its efficiency in BTU per watt-hour, so at an illustrative EER of 12 the draw is 10,000 ÷ 12 = 833 watts, which is 0.83 kWh in an hour. That is 28 percent of the naive answer, and getting it wrong overstates the running cost by more than three times.

Where the conversion earns its keep is fuel comparison. Because a therm is exactly 100,000 BTU, one therm is 29.31 kWh of raw energy, and a gallon of propane at the 91,452 BTU heat content EIA publishes is 26.80 kWh. Those figures are energy content only — they say nothing about how much of that energy reaches your rooms, which is a question of furnace AFUE or heat pump COP rather than of unit conversion. When you want that comparison with efficiency applied, the gas-vs-electric-heating-calculator is the tool that does it; when you want dollars from a genuine electrical figure, use the electricity-cost-calculator.

Frequently asked questions