kW to BTU Conversion Calculator & Formula

This calculator converts power in kilowatts (kW) to BTU per hour (BTU/h), the unit commonly used for heating and cooling equipment in the US. Enter the power in kW and you get the equivalent BTU/h, plus the reverse conversion for convenience. The result uses the standard international definition: 1 kW = 3,412.142 BTU/h.

Formula

The conversion is a simple multiplication:

BTU/h = kW × 3,412.142

Where:

• kW = power in kilowatts (1 kW = 1,000 watts)
• BTU/h = power in British thermal units per hour
• 3,412.142 = the exact conversion factor (1 kW = 3,412.142 BTU/h)

The reverse formula is: kW = BTU/h ÷ 3,412.142

Worked Example

Using the default value of 3.5 kW (a common size for a small space heater or a window air conditioner):

1. Start with the formula: BTU/h = kW × 3,412.142
2. Plug in 3.5 kW: BTU/h = 3.5 × 3,412.142
3. Multiply: 3.5 × 3,412.142 = 11,942.497
4. Rounded to the nearest whole number: 11,942 BTU/h

The calculator shows 11,942 BTU/h, which matches. For reference, a typical 3.5 kW air conditioner is often labeled as “12,000 BTU� – manufacturers round to the nearest thousand for marketing.

Why This Conversion Matters

In most of the world, power ratings for heaters, air conditioners, and heat pumps are given in kilowatts. In the United States, the same equipment is usually rated in BTU per hour. If you are comparing an American-made unit with an imported one, or reading a manual from another country, you need to convert between the two. The conversion is also essential for sizing a room: a common rule of thumb is that you need about 20 BTU/h per square foot of living space (roughly 63 W/m²), but that varies with insulation, climate, and ceiling height.

How to Choose the Right Unit

When choosing a heater or air conditioner, the power rating tells you how much heat it can add or remove per hour. For heating, a higher BTU/h means a warmer room faster. For cooling, a higher BTU/h means faster cooling, but an oversized unit can short-cycle (turn on and off too frequently), which wastes energy and reduces dehumidification. A good starting point:

• Small room (100–150 sq ft): 5,000–6,000 BTU/h (1.5–1.8 kW)
• Medium room (150–250 sq ft): 7,000–8,000 BTU/h (2.1–2.3 kW)
• Large room (250–350 sq ft): 9,000–10,000 BTU/h (2.6–2.9 kW)
• Whole house (1,500–2,000 sq ft): 30,000–40,000 BTU/h (8.8–11.7 kW)

These are rough estimates. Always consult the manufacturer’s sizing guide or a professional for your specific situation.

Common Mistakes and Misconceptions

One frequent error is confusing BTU (a unit of energy) with BTU/h (a unit of power). A BTU is the energy needed to raise one pound of water by one degree Fahrenheit. BTU/h is the rate of energy transfer. When people say “a 12,000 BTU air conditioner,� they mean 12,000 BTU/h – the “per hour� is implied. Another mistake is using the wrong conversion factor: some sources use 3,412, others 3,412.142, and a few round to 3,413. The difference is tiny (0.03%) and rarely matters for real-world sizing, but for precise engineering calculations use the exact factor. Also, be careful with kilowatt-hours (kWh) – that is energy, not power. To convert kWh to BTU (energy), multiply by 3,412.142, but that is a different calculation than the one on this page.

Limits of the Formula

This conversion is a pure unit conversion – it is always accurate mathematically. However, it does not account for efficiency. A 3.5 kW electric heater produces exactly 11,942 BTU/h of heat (electric resistance heaters are nearly 100% efficient at converting electricity to heat). But a 3.5 kW air conditioner might have a cooling capacity of 12,000 BTU/h while consuming only 3.5 kW of electricity – that is because it moves heat rather than creating it. The conversion factor only works for the actual thermal output, not the electrical input. For heat pumps and air conditioners, you need the coefficient of performance (COP) or the energy efficiency ratio (EER) to relate electrical input to thermal output.

Frequently Asked Questions

How many BTU is 1 kW?

Exactly 3,412.142 BTU/h. For quick mental math, you can use 3,412 – the difference is less than 0.01%. So 1 kW ≈ 3,412 BTU/h.

How do I convert BTU to kW?

Divide the BTU/h by 3,412.142. For example, a 24,000 BTU/h air conditioner is 24,000 ÷ 3,412.142 ≈ 7.03 kW.

Is kW or BTU more common?

kW is the standard unit in most countries and in scientific contexts. BTU/h is primarily used in the US and Canada for heating and cooling equipment. You will often see both on product labels in North America.

What is the difference between BTU and BTU/h?

BTU is a unit of energy, like a joule or a calorie. BTU/h is a unit of power, like a watt. Power is energy per unit time. A device rated at 10,000 BTU/h transfers 10,000 BTUs of heat every hour. The two are often used interchangeably in casual conversation, but they are not the same.

Why do some heaters list watts and others BTU?

It depends on the target market. European and Asian manufacturers often list watts (or kW), while North American manufacturers list BTU/h. Some list both. For example, a 1,500 W space heater is about 5,118 BTU/h (1,500 × 3.412).

Can I use this conversion for natural gas or propane?

Yes, the conversion factor is the same for any type of power. However, for gas appliances, the rating on the label is usually the input energy (the heat content of the fuel), not the output to your room. The actual heat output is lower due to combustion efficiency. Check the efficiency rating (e.g., 80% or 95%) to get the real output.

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in kw | Power | kW | 3.5 | 0
out btu | BTU per hour | BTU/h | kw * 3412.142 | 0
out kw_back | Reverse: kW | kW | btu / 3412.142 | 2