British Thermal Units to Millijoules (BTU to mJ)
1 British thermal unit equals 1,055,055.853 millijoules (rounded).
How to convert British thermal units to millijoules
To convert British thermal units to millijoules, multiply the number of British thermal units by 1,055,055.853. The factor is rounded to 10 significant digits. To go the other way, multiply millijoules by 9.478171203×10⁻⁷ (rounded).
millijoules = British thermal units × 1,055,055.853
Example: 10 British thermal units = 10,550,558.53 millijoules.
The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.
About these units
British Thermal Unit (BTU)
The International Table BTU, exactly 1,055.05585262 joules. The energy to heat one pound of water by one degree Fahrenheit; used for heating, cooling and gas appliances in the US.
Few energy units come in as many versions as the British thermal unit. It was defined as the heat needed to raise one pound of liquid water by one degree Fahrenheit, but because water's heat capacity shifts slightly with temperature, definitions differ by up to 0.5 percent: about 1,054.35 J for the thermochemical Btu, 1,054.80 J at 59 degrees Fahrenheit (used for American natural gas pricing), 1,054.68 J at 60 degrees (mainly Canadian), and 1,059.67 J at 39 degrees. A 1942 note suggests the term apparently arose in the United States and was later adopted in Britain.
The version on this site is the International Table Btu, about 1,055.06 J, which comes from the international steam table conferences that tied heat units to the joule. Joule's own 1850 experiments gave 772.692 foot-pounds of work per Btu, the number that first linked heat to mechanical effort.
Today the Btu survives in natural gas pricing (MMBtu means a million Btu), US building energy reporting, and equipment ratings in Btu per hour. One ton of air-conditioning is 12,000 Btu/h, or 3.52 kW. A single wooden kitchen match burning releases about one Btu.
1 British thermal unit = 1,055.055853 joules (approximately).
Sources: Wikipedia: British thermal unit; Wikipedia: James Prescott Joule
Millijoule (mJ)
One thousandth of a joule. Used for very small amounts of energy.
Prefixing the joule with milli gives a unit one thousandth of the base size, so 1 mJ is 0.001 J. The joule itself honours the English physicist James Prescott Joule, and its name was proposed by Wilhelm Siemens in 1882 before adoption at the 1889 International Electrical Congress. Because the joule equals one watt-second, a millijoule is also a milliwatt applied for one second, which makes it a natural size for tiny electrical budgets.
Some verifiable comparisons show the scale. One list of energy magnitudes puts an atomic battery's output over an hour at about 3 mJ, and an LED running for a second at about 40 mJ. A half-dollar coin dropped from a metre releases roughly 110 mJ. In atomic units, one millijoule is about 6.24 x 10^15 electronvolts, using the exact electronvolt value of 1.602176634 x 10^-19 J. Below the millijoule come the microjoule and nanojoule, so it sits at the coarse end of small-energy measurement.
1 millijoule = 0.001 joules (exactly).
Sources: Wikipedia: Joule; Wikipedia: Orders of magnitude (energy); Wikipedia: Electronvolt
Related conversions
- Millijoules to British thermal units (reverse)
- British thermal units to joules
- British thermal units to kilojoules
- British thermal units to watt-hours
- British thermal units to kilowatt-hours
- British thermal units to calories
- British thermal units to kilocalories
- British thermal units to megajoules
- British thermal units to gigajoules
- British thermal units to megawatt-hours
- British thermal units to foot-pounds
- British thermal units to electronvolts
- British thermal units to kiloelectronvolts
- Joules to millijoules
- Kilojoules to millijoules
- Watt-hours to millijoules
- Kilowatt-hours to millijoules
- Calories to millijoules
- Kilocalories to millijoules
See all energy units.