What Is a Therm?
A therm is a unit of heat energy equal to exactly 100,000 British Thermal Units (BTU). It is widely used in US domestic gas billing — the monthly gas bill for a typical American household is expressed in therms. In the UK, therms appeared in older gas tariffs before metrication introduced kWh billing in the 1990s. They are still used in some commercial and industrial UK gas contracts, LNG pricing and wholesale gas trading.
kWh
BTU
MJ
m³
The Therms to kWh Formula
Unlike converting gas volume (m³ or ft³) to kWh — which requires your local calorific value — the therms to kWh conversion is a fixed mathematical relationship between two energy units. No calorific value, correction factor or regional data is needed.
Where Does 29.3001 Come From?
The conversion factor derives directly from the definitions of the two units. 1 therm = 100,000 BTU by definition. 1 kWh = 3,412.14 BTU by definition (since 1 kWh = 3.6 MJ and 1 BTU = 1,055.06 J). Therefore: 100,000 BTU ÷ 3,412.14 BTU/kWh = 29.3001 kWh per therm. This is exact and universal — it never changes regardless of gas type, supplier or country.
How to Convert Therms to kWh — Step by Step
Find Your Therms Value
Locate the number of therms on your gas bill, energy statement or data source. On US gas bills, therms appear as "Therms Used" or "CCF × Therm Factor". On older UK bills or commercial contracts, look for "therms" or "Dth" (dekatherms — multiply by 10 to get therms first).
Multiply by 29.3001
Multiply your therms value by 29.3001. The result is kilowatt hours. This single step is all that is needed — no calorific value, no correction factor, no division.
Verify Your Result
For US gas bills, your supplier may show kWh alongside therms — compare your result. For UK commercial invoices, the kWh figure should appear on the detailed line items. A difference of less than 0.1% is rounding only.
Worked Examples
≈ 0.5 m³ gas · ~£1.09
UK daily avg · ~£2.33
Cold Jan day · ~£5.43
UK avg/month · ~£71.10
Ofgem medium · ~£853/yr
1 Dth · ~£21.74
Therms to kWh Conversion Table
Quick reference table using the exact conversion factor of 29.3001 kWh/therm. Cost at Ofgem 2026 rate of 7.42p/kWh. For the reverse, use our kWh to therms converter.
| Therms | kWh | BTU | MJ | Est. Cost (7.42p) | Equiv. m³ (CV 39.5) |
|---|---|---|---|---|---|
| 0.1 | 2.930 | 10,000 | 10.55 | £0.22 | 0.26 m³ |
| 0.5 | 14.65 | 50,000 | 52.74 | £1.09 | 1.31 m³ |
| 1 | 29.30 | 100,000 | 105.48 | £2.17 | 2.62 m³ |
| 2 | 58.60 | 200,000 | 210.96 | £4.35 | 5.24 m³ |
| 5 | 146.50 | 500,000 | 527.40 | £10.87 | 13.11 m³ |
| 10 | 293.0 | 1,000,000 | 1,054.8 | £21.74 | 26.22 m³ |
| 20 | 586.0 | 2,000,000 | 2,109.6 | £43.48 | 52.43 m³ |
| 32.7 | 958.1 | 3,270,000 | 3,449.2 | £71.10 | 85.78 m³ |
| 50 | 1,465.0 | 5,000,000 | 5,274.0 | £108.70 | 131.1 m³ |
| 100 | 2,930.0 | 10,000,000 | 10,548 | £217.41 | 262.2 m³ |
| 200 | 5,860.0 | 20,000,000 | 21,096 | £434.81 | 524.3 m³ |
| 392.5 | 11,505 | 39,250,000 | 41,400 | £853.67 | 1,029 m³ |
| 500 | 14,650 | 50,000,000 | 52,740 | £1,087 | 1,311 m³ |
| 1,000 | 29,300 | 100,000,000 | 105,480 | £2,174 | 2,622 m³ |
m³ equivalent uses CV 39.5 kWh/m³ and VCF 1.02264. Cost excludes standing charge and VAT. 392.5 therms ≈ Ofgem medium annual consumption (11,500 kWh/year).
↔ Need the Reverse? Convert kWh Back to Therms
Use our kWh to therms converter — or try our full gas calculator suite for UK meter readings in m³ or ft³.
Where Therms Are Used in 2026
United States Gas Billing
The therm is the standard unit for domestic natural gas billing in the United States. Every US utility company — from National Grid US to Atmos Energy — bills residential customers in therms per month. A typical US home uses 50–75 therms per month in winter and 5–10 therms per month in summer, totalling 500–700 therms per year (approximately 14,650–20,510 kWh/year).
UK Commercial Gas Contracts
While UK domestic gas has been billed in kWh since 1999, commercial and industrial gas contracts in the UK frequently reference therms or dekatherms (Dth). Large industrial users, commercial boilers, combined heat and power (CHP) plants and gas-fired power stations may see therms-based pricing in their supply contracts. The UK's National Balancing Point (NBP) wholesale gas market historically quoted prices in pence per therm (p/therm) — though kWh and MWh have become more common in recent years.
Energy Performance Calculations
Building energy auditors, mechanical and electrical (M&E) engineers and HVAC designers sometimes work with therms when specifying heating plant from US manufacturers or reviewing US-originated energy models. Converting therms to kWh is essential when comparing with UK EPC ratings, Ofgem benchmarks or CIBSE design guides, all of which use kWh.
Therms, m³ and kWh — Quick Comparison
All three are valid ways to express natural gas energy — but only kWh is used for UK domestic billing today. This table shows the relationship between all three for context.
| Unit | Type | = kWh | Used Where | Conversion |
|---|---|---|---|---|
| 1 therm | Energy | 29.3001 kWh | US billing, UK commercial | × 29.3001 |
| 1 dekatherm | Energy | 293.001 kWh | Wholesale gas, LNG | × 293.001 |
| 1 m³ gas | Volume | ≈ 11.18 kWh | UK domestic billing | × CV × 1.02264 ÷ 3.6 |
| 1 ft³ gas | Volume | ≈ 0.317 kWh | Older UK imperial meters | × 0.0283 × CV × 1.02264 ÷ 3.6 |
| 1 MWh | Energy | 1,000 kWh | Commercial contracts | ÷ 1,000 |
| 1 GJ | Energy | 277.78 kWh | Industrial, LNG | × 277.78 |
| 1 MMBTU | Energy | 293.001 kWh | US/global wholesale | × 293.001 |
UK Regional Calorific Values 2026
While the therms-to-kWh conversion itself doesn't need a calorific value, you may need the CV if you're also working with UK m³ meter readings alongside your therms data — for example, when cross-referencing a US energy model with UK meter readings. The table below shows 2026 regional CVs for reference.
| UK Region | CV Range (kWh/m³) | Band | Therms per m³ | m³ per therm |
|---|---|---|---|---|
| 🇬🇧 UK National Average | 38.5 – 40.5 | Average | 0.381 | 2.62 m³ |
| London & South East | 39.0 – 41.5 | Above Avg | 0.389 | 2.57 m³ |
| South West England | 38.8 – 41.0 | Average | 0.385 | 2.60 m³ |
| East Midlands | 39.0 – 40.8 | Average | 0.385 | 2.60 m³ |
| West Midlands | 38.5 – 40.5 | Average | 0.381 | 2.62 m³ |
| Yorkshire & Humber | 38.0 – 40.2 | Average | 0.379 | 2.64 m³ |
| North West England | 37.8 – 40.0 | Below Avg | 0.377 | 2.65 m³ |
| North East England | 37.5 – 39.8 | Below Avg | 0.374 | 2.67 m³ |
| Scotland | 37.2 – 40.0 | Below Avg | 0.376 | 2.66 m³ |
| Wales | 38.0 – 40.2 | Average | 0.379 | 2.64 m³ |
Therms/m³ = CV × 1.02264 ÷ 3.6 ÷ 29.3001. m³/therm = 29.3001 × 3.6 ÷ (CV × 1.02264). Mid-range CV used. Source: National Grid / Xoserve 2026.