How many BTU are in one kilojoule?

One kilojoule equals approximately 0.947817 International Table BTU. Conversely, 1 BTU (IT) = exactly 1.05505585262 kJ.

Which BTU definition does this tool use?

This tool uses the International Table BTU (BTU_IT), where 1 BTU = 1,055.05585262 J = 1.05505585262 kJ. Other BTU definitions, including the thermochemical BTU, use slightly different factors.

How do I convert kilojoules to BTU manually?

Multiply your kJ value by 0.947817 to get BTU. For example, 100 kJ = 94.7817 BTU. To go the other way, multiply BTU by 1.05505585 to get kJ.

What is the difference between kJ and BTU?

Both measure energy. The kilojoule (kJ) is the SI metric unit, equal to 1,000 joules. The BTU (British Thermal Unit) is an imperial unit historically defined as the heat needed to raise one pound of water by 1°F. 1 BTU ≈ 1.055 kJ.

Why do HVAC ratings use BTU instead of kJ?

The US building and HVAC industry historically used imperial units. Air conditioner and heater capacity is rated in BTU/hr (often just called "BTU"). The rest of the world typically uses watts or kilowatts. 1 watt = 3.41214 BTU/hr = 3.6 kJ/hr.

How many kJ is a typical home furnace output?

A typical residential gas furnace outputs 60,000–100,000 BTU/hr, which equals roughly 63,300–105,500 kJ/hr (or about 17.6–29.3 kW).

Kilojoules to BTU Converter

Enter kilojoules or BTU for instant bidirectional conversion. Also shows joules and a quick-reference table.

kJ ↔ BTU Converter

Kilojoules (kJ)

Joules (J)

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BTU (International Table)

BTU

1 BTU_IT = 1.05505585262 kJ

Quick Reference Table

Common kJ values in BTU (1 kJ = 0.947817 BTU)

Kilojoules (kJ)	Joules (J)	BTU

1 BTU_IT = 1.05505585262 kJ — International Table definition

HVAC power context

HVAC equipment ratings use BTU/hr (energy per hour), not BTU alone. 1 kW = 3,412.14 BTU/hr = 3,600 kJ/hr. A 12,000 BTU/hr air conditioner (1 "ton") consumes about 3.517 kW and moves 12,660 kJ/hr of heat. To convert a BTU/hr rating to kW, divide by 3,412.14.

Summary

This converter handles energy between kilojoules (kJ), joules (J), and British Thermal Units (BTU). The International Table BTU is used: 1 BTU = 1.05505585262 kJ, so 1 kJ = 0.947817 BTU. Enter any value in kJ, J, or BTU and all fields update instantly. A reference table covers the most common kJ-to-BTU pairs used in HVAC, food labeling, and heating specifications.

How it works

Enter a value in the Kilojoules field to see the BTU (and joules) equivalent instantly.
Enter a value in the BTU field to reverse-convert back to kilojoules and joules.
The Joules field also accepts input and converts in both directions.
All fields update in real time — no button click needed.
Click any row in the reference table to load that value into the converter.

Use cases

Convert HVAC or furnace energy ratings between kJ and BTU for US building specifications.
Translate food energy values from kilojoules (common outside the US) to BTU for industrial processes.
Compare boiler or hot water heater output figures given in BTU against metric kJ specs.
Convert physics or engineering homework answers between SI and imperial energy units.
Verify calorimeter or combustion measurements against BTU equivalents in US references.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu