BTU to Calories Converter

BTU to Calories

Convert btu (BTU) to calories (cal). Both measure work and power, and the conversion comes up in nutrition, electricity, fitness work.

The Formula

`` calories = btu × 252.164400722 btu = calories × 0.00396566683139 `

One BTU is 252.1644 calories, and one calory is 0.003966 btu.

Conversion Table

BTU	Calories
1 BTU	252.1644 cal
2 BTU	504.3288 cal
5 BTU	1,260.82 cal
10 BTU	2,521.64 cal
25 BTU	6,304.11 cal
50 BTU	12,608.22 cal
100 BTU	25,216.44 cal
500 BTU	126,082.2 cal
1,000 BTU	252,164.4 cal

The Other Direction

Calories	BTU
1 cal	0.003966 BTU
2 cal	0.007931 BTU
5 cal	0.019828 BTU
10 cal	0.039657 BTU
25 cal	0.099142 BTU
50 cal	0.198283 BTU
100 cal	0.396567 BTU
500 cal	1.9828 BTU
1,000 cal	3.9657 BTU

What Each Unit Is

BTU (BTU) — the energy to raise one pound of water by one degree Fahrenheit, or 1,055 joules. The imperial thermal unit, still standard for US heating, cooling and gas.

Calories (cal) — the energy to raise one gram of water by one degree Celsius, or 4.184 joules — the "small" calorie. A 19th-century thermal unit, displaced by the joule in physics but retained in nutrition.

A Sense of Scale

• A window air conditioner is 5,000–12,000 BTU/h
• US furnaces are rated in BTU
• A gram of sugar holds about 4,000 small calories

Precision

The factor 252.164400722 is rounded. For engineering work carry more digits than the table above, and round only at the end — rounding at each step compounds.

Watch Out For

• Food labels say "calorie" but mean kilocalorie — 1,000 of these. A 200-calorie snack is 200 kcal, or 837 kJ.

In Code

`javascript const btuToCalorie = (value) => value * 252.164400722; ``

Where This Conversion Comes Up

• Nutrition
• Electricity
• Fitness
• Heating
• Fuel

How Many Decimals Do You Need?

Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 BTU with the factor truncated at each decimal place:

Decimals kept	Factor	137 BTU becomes	Error
0	252	34,524	0.0652%
1	252.2	34,551.4	0.0141%
2	252.16	34,545.92	0.0017%
3	252.164	34,546.47	0.0002%
4	252.1644	34,546.52	—

A rule that holds for any conversion: round once, at the end. Rounding the factor and then multiplying compounds the error through every subsequent calculation, while carrying full precision and rounding the final answer does not.

The right number of significant figures is set by your input, not by the converter. If you measured btu to three significant figures, the answer in calories is only good to three — writing more digits claims precision the measurement never had.