How many BTU in a ton?

12,000 BTU per hour. NIST lists the "ton of refrigeration (12 000 Btu_IT/h)" as 3,516.853 W, so one ton of cooling is 3.52 kW. Wikipedia gives the origin: it is "the rate of heat transfer needed to freeze 1 short ton (907 kg) of water into ice in 24 hours."

How do I convert BTU to tons?

Divide BTU per hour by 12,000. 18,000 BTU/h is 1.5 tons, 24,000 is 2, 30,000 is 2.5 and 36,000 is 3. To go back, multiply tons by 12,000: 3.5 tons is 42,000 BTU/h.

How many tons is a 36,000 BTU air conditioner?

3 tons: 36,000 / 12,000. In kW it is 10.55 kW (BTU/h / 3,412.142).

How many square feet does one ton of AC cool?

On the ENERGY STAR room chart, 12,000 BTU/h (one ton) covers rooms up to 550 sq ft and two tons (24,000 BTU/h) up to 1,500 sq ft. There is no single square feet per ton figure: at the top of each band it runs from 360 sq ft per ton for the smallest band to 882 for the largest (table 2). For a whole house a Manual J load calculation replaces the chart.

How many tons of AC for 1,500 sq ft?

Read as one open space, 1,500 sq ft is in the chart's "1,500 up to 2,000" band: 30,000 BTU/h, 2.5 tons. Room by room the same house adds up to more, because every room gets at least the chart's smallest figure; the 1,500 sq ft house guide shows both readings.

What is a ton of cooling in kW and watts?

3.52 kW, or 3,517 W. The factor is 1 W = 3.412142 BTU/h (Wikipedia, British thermal unit; NIST prints the same factor the other way round, 1 BTU/h = 0.2930711 W).

BTU to tons converter (and square feet per ton of AC)

One ton of cooling is 12,000 BTU per hour, which is 3.52 kW. To convert BTU to tons, divide BTU per hour by 12,000; to convert tons to BTU, multiply by 12,000. Type a figure in any box below and the other two follow. Under the converter: 1.5 to 5 tons in BTU/h and kW, and the floor area each size covers on the ENERGY STAR room air conditioner chart.

BTU per hour (BTU/h)Starting value: 12,000 BTU/h, one ton (NIST, Guide to the SI, Appendix B.9, power). Type in any box.Tons of coolingKilowatts (kW)

Result

Tons of cooling: 1 ton
BTU per hour: 12,000 BTU/h
Kilowatts: 3.517 kW
Watts: 3,517 W
ENERGY STAR room chart: Up to 550 sq ft as one open space

1 ton = 12,000 BTU/h; 1 W = 3.412142 BTU/h. The chart line reads the ENERGY STAR room air conditioner chart backwards (8 ft ceiling, average sun, two people): a first estimate for one space, not a Manual J load calculation for a house.

1. How to convert BTU to tons, and back

Tons = BTU per hour / 12,000. BTU per hour = tons x 12,000. kW = BTU per hour / 3,412.142, because 1 W is 3.412142 BTU/h. NIST lists the "ton of refrigeration (12 000 Btu_IT/h)" as 3,516.853 W. The 12,000 is the definition of the unit: Wikipedia explains it as "the rate of heat transfer needed to freeze 1 short ton (907 kg) of water into ice in 24 hours."

So 9,000 BTU/h is 0.75 tons, 18,000 is 1.5, 24,000 is 2 and 36,000 is 3. A ton is a rate, not a weight: the heat a unit removes per hour.

2. 1.5 to 5 tons: BTU/h, kW and the area on the room chart

The last column reads the ENERGY STAR room air conditioner chart backwards: each size covers every band whose figure is at or below it, and the column shows the area it adds over the size above it in the table. ENERGY STAR: "The capacities are calculated based on an 8-foot ceiling." This is a chart for one space with average sun and two people, not a Manual J load calculation for a whole house. It stops at 2,500 sq ft (34,000 BTU/h), so 3.5, 4 and 5 tons are beyond it.

Table 1: 1.5 to 5 tons in BTU/h and kW, and the floor area each covers on the ENERGY STAR room chart (one open space, 8 ft ceiling)
Tons	BTU/h	kW	Area on the chart (sq ft)
1.5	18,000	5.28	up to 1,000
2	24,000	7.03	1,000 up to 1,500
2.5	30,000	8.79	1,500 up to 2,000
3	36,000	10.55	2,000 up to 2,500
3.5	42,000	12.31	beyond the chart (it stops at 2,500)
4	48,000	14.07	beyond the chart (it stops at 2,500)
5	60,000	17.58	beyond the chart (it stops at 2,500)

Read as one open space, a 1,500 sq ft house is 30,000 BTU/h, 2.5 tons. A house is not one room: the 1,500 sq ft house guide adds the rooms up and explains why the total is higher. For one room with the chart's sun, people and kitchen adjustments, use the AC BTU calculator; for the next size a mini split maker sells, the mini split size guide.

3. Tons to square feet, band by band

To answer "how many square feet per ton", turn the chart around: divide the top of each band by its tons. The result is not one number. It runs from 360 sq ft per ton for the smallest band (100 up to 150 sq ft, 5,000 BTU/h) to 882 for the largest (2,000 up to 2,500 sq ft, 34,000 BTU/h), because the chart's BTU per square foot falls as the space grows. We do not print a single square feet per ton rule: the chart does not give one.

Table 2: the ENERGY STAR room chart in tons and kW, with square feet per ton at the top of each band
Area (sq ft)	BTU/h	Tons	kW	Sq ft per ton (top of band)
100 up to 150	5,000	0.42	1.47	360
150 up to 250	6,000	0.50	1.76	500
250 up to 300	7,000	0.58	2.05	514
300 up to 350	8,000	0.67	2.34	525
350 up to 400	9,000	0.75	2.64	533
400 up to 450	10,000	0.83	2.93	540
450 up to 550	12,000	1.00	3.52	550
550 up to 700	14,000	1.17	4.10	600
700 up to 1,000	18,000	1.50	5.28	667
1,000 up to 1,200	21,000	1.75	6.15	686
1,200 up to 1,400	23,000	1.92	6.74	730
1,400 up to 1,500	24,000	2.00	7.03	750
1,500 up to 2,000	30,000	2.50	8.79	800
2,000 up to 2,500	34,000	2.83	9.96	882

One ton (12,000 BTU/h) covers rooms up to 550 sq ft on the chart; two tons cover up to 1,500 sq ft. A garage is not a room in a home, so its figures need more care: see the garage BTU guide for heating and cooling one.

Frequently asked questions

How many BTU in a ton?: 12,000 BTU per hour. NIST lists the "ton of refrigeration (12 000 Btu_IT/h)" as 3,516.853 W, so one ton of cooling is 3.52 kW. Wikipedia gives the origin: it is "the rate of heat transfer needed to freeze 1 short ton (907 kg) of water into ice in 24 hours."
How do I convert BTU to tons?: Divide BTU per hour by 12,000. 18,000 BTU/h is 1.5 tons, 24,000 is 2, 30,000 is 2.5 and 36,000 is 3. To go back, multiply tons by 12,000: 3.5 tons is 42,000 BTU/h.
How many tons is a 36,000 BTU air conditioner?: 3 tons: 36,000 / 12,000. In kW it is 10.55 kW (BTU/h / 3,412.142).
How many square feet does one ton of AC cool?: On the ENERGY STAR room chart, 12,000 BTU/h (one ton) covers rooms up to 550 sq ft and two tons (24,000 BTU/h) up to 1,500 sq ft. There is no single square feet per ton figure: at the top of each band it runs from 360 sq ft per ton for the smallest band to 882 for the largest (table 2). For a whole house a Manual J load calculation replaces the chart.
How many tons of AC for 1,500 sq ft?: Read as one open space, 1,500 sq ft is in the chart's "1,500 up to 2,000" band: 30,000 BTU/h, 2.5 tons. Room by room the same house adds up to more, because every room gets at least the chart's smallest figure; the 1,500 sq ft house guide shows both readings.
What is a ton of cooling in kW and watts?: 3.52 kW, or 3,517 W. The factor is 1 W = 3.412142 BTU/h (Wikipedia, British thermal unit; NIST prints the same factor the other way round, 1 BTU/h = 0.2930711 W).

Sources

NIST, NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science (updated August 18, 2025), read 2026-10-19.
Wikipedia, British thermal unit (undated), read 2026-10-19.
ENERGY STAR (U.S. EPA), Room Air Conditioners: the room size to capacity chart (undated), read 2026-10-19.

Every figure on this page is computed by the converter's own code from these documents. The chart readings are for a room air conditioner in one space, not a load calculation for a house.

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Last updated 2026-10-19. Sizing estimates from published charts and rules of thumb (ENERGY STAR, manufacturer guides), each with its source and date: a Manual J load calculation by an installer is the final word.