Understanding British Thermal Units (IT) to US Therms Conversion
The British Thermal Unit (IT) equals 1055.056 joules and is the base heat unit on gas meters and appliance labels. The US therm is defined as exactly 100,000 BTU (IT), or about 105.5 megajoules, and is the unit natural-gas utilities in the United States use for billing. Converting BTU to therms is essential for reading gas bills and sizing residential and commercial heating loads.
Conversion Formula
To convert British Thermal Units (IT) to US Therms, multiply by this factor:
Step-by-Step Example
Convert 25 British Thermal Units (IT) to US Therms.
How to Convert British Thermal Units (IT) to US Therms
Because a therm is essentially 100,000 BTU, the conversion is a straightforward scaling.
- Note the BTU amount: Begin with energy in British Thermal Units (IT).
- Multiply by the factor: Use 0.00001000239 therms per BTU.
- Sanity-check: Roughly dividing by 100,000 should give nearly the same answer.
- Report the value: thm.
British Thermal Units (IT) to US Therms conversion table
| British Thermal Units (IT) (BTU) | US Therms (thm) |
|---|---|
| 0 | 0 |
| 1 | 0.00001000239 |
| 2 | 0.00002000478 |
| 3 | 0.00003000716 |
| 4 | 0.00004000955 |
| 5 | 0.00005001194 |
| 6 | 0.00006001433 |
| 7 | 0.00007001671 |
| 8 | 0.0000800191 |
| 9 | 0.00009002149 |
| 10 | 0.0001000239 |
| 15 | 0.0001500358 |
| 20 | 0.0002000478 |
| 25 | 0.0002500597 |
| 30 | 0.0003000716 |
| 40 | 0.0004000955 |
| 50 | 0.0005001194 |
| 60 | 0.0006001433 |
| 70 | 0.0007001671 |
| 80 | 0.000800191 |
| 90 | 0.0009002149 |
| 100 | 0.001000239 |
| 150 | 0.001500358 |
| 200 | 0.002000478 |
| 250 | 0.002500597 |
| 300 | 0.003000716 |
| 400 | 0.004000955 |
| 500 | 0.005001194 |
| 600 | 0.006001433 |
| 700 | 0.007001671 |
| 800 | 0.00800191 |
| 900 | 0.009002149 |
| 1000 | 0.01000239 |
| 2000 | 0.02000478 |
| 3000 | 0.03000716 |
| 4000 | 0.04000955 |
| 5000 | 0.05001194 |
| 10000 | 0.1000239 |
| 25000 | 0.2500597 |
| 50000 | 0.5001194 |
| 100000 | 1.000239 |
| 250000 | 2.500597 |
| 500000 | 5.001194 |
| 1000000 | 10.00239 |
What is the British Thermal Unit (IT)?
The British thermal unit (IT) is a unit of energy in the imperial and US customary systems, defined as roughly the heat needed to raise the temperature of one pound of water by one degree Fahrenheit. It is widely used in heating, cooling, and the power industries.
Definition
The "IT" (International Steam Table) British thermal unit is defined exactly in terms of the SI joule.
The exact value is 1 BTU (IT) = 1055.05585262 J. This IT definition is fixed by convention (derived from 1 BTU_IT = 1055.05585262 J, i.e. based on the International Steam Table calorie of 4.1868 J). It differs slightly from the thermochemical BTU (1054.35 J) and the mean BTU, because the amount of heat to warm water depends on the starting temperature.
Origin and History
The BTU arose in the 19th century alongside the calorie as engineers sought a practical unit tied to water and everyday temperature scales. Multiple definitions emerged (39 °F, 60 °F, mean, thermochemical), and the International Steam Table conference of 1956 fixed the IT calorie, and hence the IT BTU, to a precise joule value.
Law and Notable Facts
In the United States, air conditioners and furnaces are rated in BTU per hour, and natural gas is sold in therms (1 therm = 100,000 BTU). One "ton" of cooling equals 12,000 BTU/h, historically the heat absorbed by melting one short ton of ice in 24 hours.
Real-World Examples and Conversions
- 1 BTU ≈ 1055 J ≈ 0.293071 watt-hour; a 5000 BTU/h window air conditioner draws about 1465 W of cooling.
- 1 BTU is roughly the energy released by burning one wooden match.
- 1 kWh = 3412.14 BTU, and 1 therm = 105.506 MJ.
What is the US Therm?
The US therm is a unit of heat energy used primarily in the natural gas industry to measure and bill the energy content of gas supplied to homes and businesses in the United States.
Definition
The US therm is defined as 100,000 British thermal units (BTU) based on the 59 °F (15 °C) BTU:
More precisely, the US therm equals exactly 105,480,400 joules (about 105.48 MJ). It should not be confused with the slightly larger UK therm, which is based on the International Table BTU and equals 105,505,585.257 J.
Origin and History
The therm entered use in the 20th century as gas utilities shifted from billing customers by volume to billing by delivered energy, since the heating value of natural gas varies with its composition. Combining "therm" (from the Greek thermē, heat) with a fixed BTU count gave a convenient billing unit roughly equal to the energy in 100 cubic feet of typical natural gas.
Law and Notable Facts
In the United States the therm is a legally recognized commercial unit for natural gas sales. Gas meters record volume in hundreds of cubic feet (ccf), which utilities multiply by a "therm factor" reflecting the gas's actual heat content to convert to therms for billing.
Real-World Examples and Conversions
- A typical US home uses roughly 500 to 1,000 therms of natural gas per year for heating, cooking, and hot water.
- 1 therm equals about 29.3 kilowatt-hours of energy.
- Burning 1 therm of natural gas releases approximately 105.5 MJ of heat, enough to run a 20 kW furnace at full output for about 88 minutes.
Frequently Asked Questions
How many therms is one BTU?
One BTU (IT) is about 0.00001000239 US therms, because a US therm is defined as 100,000 BTU.
Why isn't the factor exactly 1/100,000?
The US therm is officially tied to 100,000 BTU (59 °F), which differs infinitesimally from the IT BTU, so the ratio is 0.00001000239 rather than exactly 0.00001.
How many BTU are in a therm?
One US therm equals about 99,976.13 IT BTU, effectively 100,000 BTU for practical billing purposes.
How does this help with my gas bill?
Utilities meter gas in therms; converting appliance BTU ratings to therms lets you estimate how much of a billed therm each appliance consumes per hour.
What is 25 BTU in therms?
25 BTU equals about 0.000250060 therms, a negligible fraction of a single billed therm.
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Complete British Thermal Units (IT) conversion table
| Unit | Result |
|---|---|
| Watt-seconds (Ws) | 1055.056 Ws |
| Watt-minutes (Wm) | 17.58426 Wm |
| Watt-hours (Wh) | 0.2930711 Wh |
| Milliwatt-hours (mWh) | 293.0711 mWh |
| Kilowatt-hours (kWh) | 0.0002930711 kWh |
| Megawatt-hours (MWh) | 2.930711e-7 MWh |
| Gigawatt-hours (GWh) | 2.930711e-10 GWh |
| Joules (J) | 1055.056 J |
| Kilojoules (kJ) | 1.055056 kJ |
| Megajoules (MJ) | 0.001055056 MJ |
| Gigajoules (GJ) | 0.000001055056 GJ |
| US Therms (thm) | 0.00001000239 thm |
| Electronvolts (eV) | 6.585141e+21 eV |
| Ergs (erg) | 10550560000 erg |
| Foot-pounds (ft-lbf) | 778.1693 ft-lbf |
| Tonnes of TNT (t-tnt) | 2.521644e-7 t-tnt |
| calories (cal) | 252.1644 cal |
| Kilocalories (kcal) | 0.2521644 kcal |