Understanding US Therms to British Thermal Units (IT) Conversion
The US therm (thm) is an energy unit used in the natural-gas industry, defined as 100,000 British thermal units and roughly the heat content of about 100 cubic feet of natural gas. The British Thermal Unit (IT), the International Table BTU, is the amount of energy needed to raise one pound of water by one degree Fahrenheit, standardized as exactly 1055.05585262 joules. Converting US therms to BTU (IT) is common on utility bills, where gas consumption is metered in therms but appliance ratings are given in BTU.
Conversion Formula
To convert US Therms to British Thermal Units (IT), multiply by this factor:
Step-by-Step Example
Convert 25 US Therms to British Thermal Units (IT).
How to Convert US Therms to British Thermal Units (IT)
Turn a natural-gas therm reading into BTU with a single factor.
- Read your therm value: Take the gas quantity in US therms, often from a utility bill.
- Multiply by the factor: Multiply by 99,976.13 BTU (IT) per therm.
- Interpret the total: The result is the equivalent energy in BTU (IT), near 100,000 per therm.
- Worked result: 25 therms × 99,976.13 = 2,499,403 BTU (IT).
US Therms to British Thermal Units (IT) conversion table
| US Therms (thm) | British Thermal Units (IT) (BTU) |
|---|---|
| 0 | 0 |
| 1 | 99976.13 |
| 2 | 199952.3 |
| 3 | 299928.4 |
| 4 | 399904.5 |
| 5 | 499880.6 |
| 6 | 599856.8 |
| 7 | 699832.9 |
| 8 | 799809 |
| 9 | 899785.2 |
| 10 | 999761.3 |
| 15 | 1499642 |
| 20 | 1999523 |
| 25 | 2499403 |
| 30 | 2999284 |
| 40 | 3999045 |
| 50 | 4998806 |
| 60 | 5998568 |
| 70 | 6998329 |
| 80 | 7998090 |
| 90 | 8997852 |
| 100 | 9997613 |
| 150 | 14996420 |
| 200 | 19995230 |
| 250 | 24994030 |
| 300 | 29992840 |
| 400 | 39990450 |
| 500 | 49988060 |
| 600 | 59985680 |
| 700 | 69983290 |
| 800 | 79980900 |
| 900 | 89978520 |
| 1000 | 99976130 |
| 2000 | 199952300 |
| 3000 | 299928400 |
| 4000 | 399904500 |
| 5000 | 499880600 |
| 10000 | 999761300 |
| 25000 | 2499403000 |
| 50000 | 4998806000 |
| 100000 | 9997613000 |
| 250000 | 24994030000 |
| 500000 | 49988060000 |
| 1000000 | 99976130000 |
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.
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.
Frequently Asked Questions
How many BTU (IT) are in one US therm?
One US therm equals about 99,976.13 BTU (IT). The US therm is defined against the 59 °F BTU, so it is just shy of the round 100,000 BTU (IT) figure.
How do I convert US therms to BTU?
Multiply the number of therms by 99,976.13. For example, 4 therms equal about 399,904.5 BTU (IT).
How many therms make one BTU (IT)?
One BTU (IT) is about 0.00001000239 US therms, the reciprocal of the conversion factor.
Why isn't a therm exactly 100,000 BTU?
A US therm is defined as 100,000 BTU based on the 59 °F BTU; expressed in International Table BTU it comes out to 99,976.13, a small definitional difference.
Where is this conversion used?
It appears on natural-gas utility bills, where consumption is measured in therms while furnace and appliance heat outputs are rated in BTU.
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Complete US Therms conversion table
| Unit | Result |
|---|---|
| Watt-seconds (Ws) | 105480400 Ws |
| Watt-minutes (Wm) | 1758007 Wm |
| Watt-hours (Wh) | 29300.11 Wh |
| Milliwatt-hours (mWh) | 29300110 mWh |
| Kilowatt-hours (kWh) | 29.30011 kWh |
| Megawatt-hours (MWh) | 0.02930011 MWh |
| Gigawatt-hours (GWh) | 0.00002930011 GWh |
| Joules (J) | 105480400 J |
| Kilojoules (kJ) | 105480.4 kJ |
| Megajoules (MJ) | 105.4804 MJ |
| Gigajoules (GJ) | 0.1054804 GJ |
| British Thermal Units (IT) (BTU) | 99976.13 BTU |
| Electronvolts (eV) | 6.583569e+26 eV |
| Ergs (erg) | 1054804000000000 erg |
| Foot-pounds (ft-lbf) | 77798350 ft-lbf |
| Tonnes of TNT (t-tnt) | 0.02521042 t-tnt |
| calories (cal) | 25210420 cal |
| Kilocalories (kcal) | 25210.42 kcal |