My server room has 15 racks each drawing 8 kW. What BTU/h cooling capacity do I need?

15 × 8,000 W = 120,000 W × 3.412 = 409,440 BTU/h. Add 10–20% headroom; you need at least a 450,000 BTU/h (37.5-ton) cooling system.

A window AC is rated 12,000 BTU/h. How many watts of cooling is that?

12,000 BTU/h ÷ 3.412 = 3,516 W of cooling capacity. The AC itself draws less electricity (about 1,200 W) because it pumps heat rather than generating it — hence a COP of about 3.

My workshop has LED lighting at 800 W, a compressor at 2,200 W, and a dust collector at 1,100 W. How much heat load is that?

Total: 4,100 W × 3.412 = 13,989 BTU/h. A 1.5-ton (18,000 BTU/h) mini-split AC would comfortably handle this plus outdoor heat gain.

Is the watt-to-BTU/h conversion exact?

Very nearly: 1 BTU is defined as exactly 1055.05585262 J. 1 BTU/h = 1055.05585262 ÷ 3600 = 0.29307107 W, so 1 W = 3.41214 BTU/h to six significant figures.

Watts to BTU/hour Converter

Enter a value to instantly convert between power units.

From

Precision4 dp

1 Watt = 3.4121 BTU/hour

Key Formulas

Kilowatt → Horsepower (mech)

hp = kW × 1.34102

Horsepower (mech) → Kilowatt

kW = hp × 0.7457

Watt → Kilowatt

kW = W × 0.001

Kilowatt → Watt

W = kW × 1000

Formula

BTU/h = W × 3.41214

HVAC equipment in North America is rated in BTU/hour, but electrical power draws and heat output of servers, motors, and lighting are measured in watts. Data center engineers routinely convert watt dissipation to BTU/h to size cooling systems — a rack of servers drawing 10,000 W generates 34,121 BTU/h of heat that the air handling unit must remove. The same logic applies to sizing a room air conditioner against the heat output of occupants and equipment.

Source: NIST SP 811, Table B.8

Last reviewed: 2026-06-11 · see our methodology

Frequently Asked Questions

Real-World Examples

A 1000 W electric space heater produces 3,412 BTU/h of heat output — slightly less than the smallest window AC unit's cooling capacity.

1000 W = 3412 BTU/h

A 3,516 W electrical load in a server room produces 12,000 BTU/h — exactly 1 ton of cooling required from the HVAC system.

3516 W = 12000 BTU/h

A person at rest generates about 150 W of body heat = 512 BTU/h — relevant when sizing office HVAC for occupancy loads.

150 W = 512 BTU/h

A full server rack drawing 10,000 W generates 34,121 BTU/h — requiring a dedicated precision air cooling unit in a data center.

10000 W = 34121 BTU/h

kw to hp hp to kw watts to kw kw to watts mw to kw kw to mw

Watts to BTU/hour Converter

Key Formulas

Formula

Frequently Asked Questions

Real-World Examples

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