How many BTU are in 1 therm?

1 US therm is defined as exactly 100,000 BTU (International Table). This tool uses 1 BTU (IT) = 1055.05585262 J to maintain precision.

What is the difference between a US therm and a UK/EC therm?

A US therm is exactly 100,000 BTU (IT). A UK/EC therm is defined directly in joules (~105.5056 MJ), which is almost the same but not identical. For billing, choose the standard your utility uses.

Can I convert BTU back to therms?

Yes. Switch to the BTU → Therm tab, enter BTU and pick the therm definition. The calculator will return therms with the same precision.

Therms to BTU Converter (therm ⇄ BTU)

Quick reference table

Therms (US)	BTU (IT)	kBTU
0.1	10000	10
0.5	50000	50
1	100000	100
5	500000	500
10	1000000	1000

How conversion works

1 US therm = 100,000 BTU (IT)

So: BTU = therms × 100,000

And: therms = BTU ÷ 100,000

When using UK/EC therm, we first go through joules: therm_J ÷ BTU_J.

Why different therms and BTU?

Energy units were standardized at different times. Utilities may specify “therm (US)” or “therm (EC)” and use slightly different BTU bases. This calculator exposes those so you can match invoices, engineering handbooks, or government documentation.

FAQ

1. Which option should I pick for US natural gas billing?

Pick “US therm (100,000 BTU IT)” and “BTU (IT)”. That’s the convention used by many US suppliers.

2. What is kBTU?

kBTU = 1,000 BTU. It’s just a scaled version often used on energy reports; 1 therm = 100 kBTU.

3. Can I convert therms directly to kWh?

Not on this page, but the relationship is: 1 therm (US) ≈ 29.30011111 kWh. You can add that to your worksheet if needed.