Convert kWh to Therms
One therm is 29.3071 kWh, so a kilowatt-hour is 0.03412 therms. The arithmetic is one division, but the therm is unlike most units a converter handles: it is not a unit of physics that someone chose to define, it is a billing unit, and it almost always arrives attached to a gas bill. That brings two things with it that a bare converter will not tell you — there are two therms in circulation, and the energy figure you have just converted carries a calorific basis that decides whether your emissions answer is right or 10.8% wrong.
To convert kilowatt-hours to therms, divide by 29.3071. So 500 kWh = 17.06 therms. To go the other way, multiply by 29.3071 — 100 therms is 2,931 kWh. A therm is defined as 100,000 International Table BTU, which is 105.5056 MJ.
therms = kWh ÷ 29.3071 (× 0.0341214). Reverse: kWh = therms × 29.3071. It comes from the therm’s definition: 100,000 BTU × 1,055.05585262 joules per BTU = 105,505,585.262 joules, divided by the 3,600,000 joules in a kilowatt-hour. Every step is a defined quantity rather than a measured one, so the conversion carries no uncertainty even though the decimal never terminates.
| kWh | ÷ 29.3071 | therms |
|---|---|---|
| 1 kWh | ÷ 29.3071 | 0.03412 therms |
| 29.3071 kWh | ÷ 29.3071 | 1 therm exactly |
| 100 kWh | ÷ 29.3071 | 3.412 therms |
| 500 kWh | ÷ 29.3071 | 17.06 therms |
How to convert kWh to therms
Divide by 29.3071 going to therms, multiply coming back. A UK household on the regulator’s medium consumption benchmark uses about 11,500 kWh of gas a year, which is 392 therms. Running it the other way, a US home heating with gas typically burns somewhere between 500 and 700 therms a year, so a 600-therm winter is 600 × 29.3071 = 17,584 kWh.
Both figures are worth holding side by side, because they are the same quantity of energy described by two national conventions rather than two different amounts of gas.
Therms to kWh — the direction a gas bill asks for
Most people meet this conversion from the therm side, holding a US gas bill and wanting a figure they can compare with an electricity bill, a heat pump quote, or a European dataset. That is the same page and the same constant: press the swap control on the converter above, or multiply by 29.3071.
The reason the reverse direction is so common is historical. British gas bills were denominated in therms until the 1990s and are now issued in kWh, with 29.3071 still printed on many bills as the legacy conversion line. American gas bills never made that move and are still issued in therms today. So the therm is simultaneously a retired unit and a current one, depending on which side of the Atlantic the bill was posted from.
kWh to therms conversion table
| kWh | → therms (÷ 29.3071) | therms | → kWh (× 29.3071) |
|---|---|---|---|
| 1 | 0.03412 | 1 | 29.31 |
| 10 | 0.3412 | 5 | 146.5 |
| 50 | 1.706 | 10 | 293.1 |
| 100 | 3.412 | 25 | 732.7 |
| 250 | 8.530 | 50 | 1,465 |
| 500 | 17.06 | 100 | 2,931 |
| 1,000 | 34.12 | 500 | 14,654 |
| 10,000 | 341.2 | 1,000 | 29,307 |
The therm belongs to a small family of units built on the same BTU, all of which follow from this one constant:
| Unit | In BTU | In kWh | Where you meet it |
|---|---|---|---|
| BTU | 1 | 0.000293071 | Appliance and HVAC ratings |
| therm | 100,000 | 29.3071 | US gas billing; legacy UK bills |
| MMBtu (= 10 therms) | 1,000,000 | 293.071 | US gas and energy trading |
| Dekatherm (= 1 MMBtu) | 1,000,000 | 293.071 | US pipeline and utility tariffs |
Two naming traps live in that table. MM means million, not “mega-mega” — it is Roman numerals, M for a thousand, twice, inherited from the oil and gas industry, so an MMBtu is a million BTU and not a trillion. And a thermie is not a therm: it is a metric unit of 4.1868 MJ, about 1.163 kWh, which is roughly a twenty-fifth of a therm. If a figure looks wrong by a factor of about 25, that is usually why.
Which therm — EC or US?
There is no single therm. It is defined as 100,000 BTU, but the British thermal unit itself has several competing definitions, so the therm inherits the ambiguity. Two are standardised and both are still quoted, and NIST lists them separately.
| Definition | Built from | Megajoules | kWh per therm | Difference |
|---|---|---|---|---|
| therm (EC) | 100,000 BTU (International Table) | 105.505585262 | 29.30711 | — used here |
| therm (US) | 100,000 BTU (59 °F) | 105.4804 | 29.30011 | −0.024% |
This converter uses the EC therm, and so should you in almost every energy context. The reason is consistency rather than preference: the International Table BTU is the definition energy statistics are built on, it is what the US Energy Information Administration and the IEA use, and it is the one the kWh to BTU conversion of 3,412.14 assumes. Using the 59 °F therm here while using the International Table BTU there would put a therm figure quietly out of step with the BTU figure it came from — the two would stop being the same energy.
Almost never on its own. The two therms are 0.024% apart, which on a 600-therm annual bill is a difference of 0.14 therms — around four kilowatt-hours a year. That is far smaller than the batch-to-batch variation in the calorific value of the gas actually delivered, and smaller still than the uncertainty in any emission factor you apply afterwards. It is worth knowing about when you are reconciling two datasets and chasing a small stubborn discrepancy of a few hundredths of a percent. It is not worth building into a model, and it is nowhere near the size of the calorific-basis question below.
A therm is energy, not a volume of gas
This is the single most common misreading of the unit, and it is worth being blunt about. A therm measures energy. It says nothing about how much gas that energy came from, and nothing about whether it came from gas at all — a therm of electricity is a perfectly meaningful quantity, it is just not something anyone bills for.
A gas meter measures volume — cubic metres in the UK, hundreds of cubic feet (ccf) in the US. The bill turns that volume into energy using the calorific value of the gas actually delivered that quarter, plus, in the UK, a volume correction for temperature and pressure. Because calorific value varies with the gas’s composition, there is no fixed conversion between cubic metres and therms. A UK therm works out at roughly 2.6 m³ and a US ccf at roughly 1.037 therms, but both figures move with the gas supply and neither belongs in a model. If you need the volume-to-energy step, take the calorific value printed on your own bill — do not use this converter for it.
The practical consequence: converting a volume of gas with this page is a mistake, and so is comparing a therm figure with a cubic-metre figure without going through the calorific value first. What this page does is exact and unit-only — energy in, the same energy out.
Turning therms into emissions: the gross-versus-net trap
Most people converting therms are on their way to a carbon number, and this is where the real error lives — not in the 0.024% therm question, but in a 10.8% one.
An emission factor per unit of energy has to state which calorific basis it is measured against. Gross (higher) calorific value counts the latent heat of the water vapour produced by combustion; net (lower) calorific value does not. For natural gas the two differ by about 11%, and the same physical quantity of gas therefore carries two different per-kWh factors depending on which convention the dataset used.
| Basis | kg CO₂e per kWh | × 29.3071 → | kg CO₂e per therm |
|---|---|---|---|
| Gross CV — the billing basis | 0.18231 | × 29.3071 | 5.34 |
| Net CV — the IPCC default basis | 0.20199 | × 29.3071 | 5.92 |
UK natural gas combustion, DEFRA, CO₂e including methane and nitrous oxide. The per-kWh values above are read live from our factor library and update when the dataset does; the per-therm column is simply that value multiplied by 29.3071.
Gas is billed on gross calorific value. A therm taken off a bill is therefore a gross-basis quantity of energy and needs a gross-basis factor. But IPCC default factors and a great deal of international energy data are published on a net basis, and they look interchangeable — both are quoted in kg CO₂e per kWh, and neither number announces its basis on the page you found it on. Apply the net factor to a billed therm and every therm is 0.58 kg CO₂e too high: 10.8% overstated, on the largest line in most organisations’ Scope 1 inventory. That error is roughly 450 times larger than the EC-versus-US therm difference this page also settles, and unlike that one it will change your conclusions. Check the basis before the factor.
This converter deliberately stops at the energy figure. Turning therms into a footprint means picking the right factor basis, deciding whether upstream fuel production is in scope, and handling more than one fuel — that is an inventory calculation, not a unit conversion. The Scope 1 combustion calculator does it properly, and the natural gas combustion methodology sets out the assumptions behind it.
Where therms turn up in emissions work
- US utility bills and tariffs. Residential and commercial gas is billed in therms across most of the United States, so any US building inventory built from bills starts here.
- Gas trading. Wholesale North American gas is priced per MMBtu or dekatherm — both exactly ten therms — so a traded volume and a billed volume are the same unit family at different scales.
- Legacy UK data. Historic British gas series and older building records are in therms, and comparing them with anything after the 1990s means passing through this conversion.
- Building benchmarking. Energy use intensity is normally expressed in kWh/m² or kBtu/ft², so a therm-denominated bill has to be converted before a building can be benchmarked against anything.
- Heating decisions. Comparing a gas boiler against a heat pump means putting therms and kilowatt-hours on one axis first — see the heat pump vs gas boiler calculator.
For the SI form of the same conversion see kWh to MJ, which is exact at ×3.6 and covers the calorific-basis question as it applies to energy generally. For the BTU the therm is built from — a hundred thousand of them — see kWh to BTU. If what you are converting is an emission intensity rather than an energy, that is a different conversion: CO₂e/kWh to /MWh and g CO₂/MJ to g CO₂/kWh.
Frequently Asked Questions
A therm is 29.3071 kWh. The figure comes from the therm’s definition as 100,000 International Table BTU, which is 105,505,585.262 joules, divided by the 3,600,000 joules in a kilowatt-hour. It is exact rather than measured, which is why UK gas bills print it to four decimal places.
Divide by 29.3071, or multiply by 0.0341214. So 500 kWh ÷ 29.3071 = 17.06 therms. To reverse it, multiply therms by 29.3071 — 100 therms is 2,931 kWh.
Not quite, though the difference is tiny. The EC therm is 100,000 International Table BTU, or 105.505585262 MJ, giving 29.30711 kWh. The US therm is 100,000 BTU measured at 59 °F, or 105.4804 MJ, giving 29.30011 kWh — lower by 0.024%. This converter uses the EC therm, because it is the definition energy statistics and the standard kWh-to-BTU conversion are built on. On a 600-therm annual bill the two differ by about four kilowatt-hours.
Because British gas bills were denominated in therms until the 1990s and are now issued in kilowatt-hours, so 29.3071 is the conversion between the old unit and the new one. It still appears on many bills and on older meter records. American bills never made the switch and are still issued in therms.
No. A therm measures energy; a cubic metre measures volume. The bridge between them is the calorific value of the gas actually delivered, which varies with its composition, so there is no fixed conversion. A UK therm works out at roughly 2.6 m³ and a US ccf at roughly 1.037 therms, but both figures move with the supply. If you need the volume-to-energy step, use the calorific value printed on your own bill.
Exactly ten, since a therm is 100,000 BTU and an MMBtu is a million. That is 293.071 kWh. A dekatherm is the same quantity under a different name. Note that MM means million here, in Roman numerals rather than SI prefixes, so an MMBtu is a million BTU and not a trillion.
About 5.34 kg CO₂e on the gross calorific value basis that gas is billed on, using the current DEFRA factor for UK natural gas combustion. Watch the basis: the same gas carries a net-calorific-value factor of about 5.92 kg CO₂e per therm, and net-basis factors are the IPCC default. Applying a net factor to a billed therm overstates emissions by 10.8%. For a full inventory figure, including whether upstream fuel production is in scope, use the Scope 1 combustion calculator rather than a per-therm multiplication.
A US home heating with natural gas typically uses somewhere between 500 and 700 therms a year, which is 14,650 to 20,500 kWh. A UK household on the regulator’s medium consumption benchmark uses about 11,500 kWh of gas, which is 392 therms. The gap is mostly climate, house size and insulation rather than a difference in the unit.