BTU per Hour to Tons Converter

One ton of cooling is 12,000 BTU per hour

The ton used in air conditioning measures a rate of heat removal, not weight. One ton of cooling moves 12,000 British thermal units per hour, which is 200 BTU per minute or about 3.52 kilowatts. ASHRAE's guide to choosing a home system puts it in one line: 1 ton = 12,000 Btu/h. ASHRAE Terminology defines the ton of refrigeration the same way and gives the metric equivalent as roughly 3,517 watts.

The number comes from ice. Melting a pound of ice absorbs 144 BTU, and a ton is 2,000 pounds, so 144 × 2,000 = 288,000 BTU of latent heat over a full day. Spread that across 24 hours and 288,000 ÷ 24 = 12,000 BTU/h. The unit survived because it matches the size of real equipment: a small window unit is 0.75 ton, a house system runs 2 to 5 tons, and a commercial chiller reaches hundreds of tons.

One naming quirk causes most of the confusion. A box that says 12,000 BTU is a 12,000 BTU/h machine, and the same shorthand appears on heaters and furnaces. The per hour part gets dropped in speech, never in the arithmetic.

Convert BTU per hour to tons with one division

Two formulas cover every case: tons = BTU/h ÷ 12,000 and BTU/h = tons × 12,000. There is no rounding step inside either one, because 12,000 is a definition rather than a measurement.

Three readings fix the direction in your head. A 24,000 BTU/h unit is 24,000 ÷ 12,000 = 2 tons. A 36,000 BTU/h unit is 36,000 ÷ 12,000 = 3 tons. A 9,000 BTU/h mini split is 9,000 ÷ 12,000 = 0.75 ton. Going back the other way, 2.5 × 12,000 = 30,000 BTU/h and 4 × 12,000 = 48,000 BTU/h.

Awkward numbers behave the same way. 15,000 ÷ 12,000 = 1.25 tons, 42,000 ÷ 12,000 = 3.5 tons, and 100,000 ÷ 12,000 = 8.3333 tons. A load calculation that lands on 34,200 BTU/h gives 34,200 ÷ 12,000 = 2.85 tons, which means buying the 3 ton unit in the catalog.

The table adds kilowatts, since a spec sheet often prints only that. One BTU/h is 0.29307107 W, so multiply by 0.00029307107 to reach kW.

Reading a nameplate in tons, BTU per hour and kilowatts

A nameplate can carry three different units for the same machine, and only one of them is capacity. Tons and BTU/h both describe cooling rate. Kilowatts on a chiller sheet may describe cooling capacity in kW or the electrical draw, and those are not the same number.

Commercial work leans on tons. A 100 ton chiller moves 100 × 12,000 = 1,200,000 BTU/h. A 500 ton plant moves 500 × 12,000 = 6,000,000 BTU/h, which is 1,758 kW of cooling. The electrical draw is much smaller, since a water cooled chiller typically uses between 0.5 and 0.6 kW per ton against 3.52 kW per ton of cooling, so read the label before you size a breaker.

Cooling towers use a different ton. The Federal Energy Management Program guide to cooling towers states the 12,000 BTU/h evaporator ton, and the ASHRAE Handbook adds the reason tower ratings run higher: every 12,000 BTU/h pulled out of the building reaches the tower with about 3,000 BTU/h of compressor heat attached, so a nominal tower ton is 15,000 BTU/h. Size the chiller on 12,000 and the tower on 15,000.

Square feet per ton and the 20 to 30 BTU rule

Contractors estimate cooling load from floor area before anyone runs a full Manual J calculation. The common range is 20 to 30 BTU/h per square foot, which is the same as 400 to 600 square feet per ton. The wide spread is climate, not sloppiness.

Hot and humid zones sit near 20 to 22 BTU/h per square foot, so 1,500 square feet needs 1,500 × 22 = 33,000 BTU/h, or 33,000 ÷ 12,000 = 2.75 tons. Mild zones run near 25, which gives 1,500 × 25 = 37,500 BTU/h and 37,500 ÷ 12,000 = 3.125 tons. Cold zones and older houses with thin insulation push toward 30, so 1,500 × 30 = 45,000 BTU/h, or 45,000 ÷ 12,000 = 3.75 tons.

Those three answers span 2.75 to 3.75 tons for the same floor plan, which is why the rule of thumb is a budget number and not a purchase order. Window count, ceiling height, attic insulation, duct leakage and the number of people in the house each move the load by half a ton or more.

What SEER2 changes, and what it leaves alone

SEER2 measures how much cooling a system delivers per watt-hour across a season, using the M1 blower test that arrived with the 2023 standards. It says nothing about capacity. A 3 ton unit is 3 tons whether the label reads 13.4 SEER2 or 20 SEER2; the difference shows up on the electric bill.

The Department of Energy minimums for split systems installed since January 1, 2023 depend on region and size. The DOE standards FAQ lists 13.4 SEER2 for the North, 14.3 SEER2 for the Southeast and Southwest below 45,000 BTU/h, and 13.8 SEER2 at 45,000 BTU/h and above in those two regions.

Efficiency turns into kilowatt-hours with one division. A 3 ton unit running 1,000 full-load hours delivers 36,000 × 1,000 = 36,000,000 BTU over the season. At 14.3 SEER2 that is 36,000,000 ÷ 14.3 ÷ 1,000 = 2,517 kWh. At the 13.4 floor it is 36,000,000 ÷ 13.4 ÷ 1,000 = 2,687 kWh. The gap is 2,687 - 2,517 = 170 kWh, which at 0.17 dollars per kWh is 170 × 0.17 = 28.90 dollars a year.

A higher SEER2 rating pays back in proportion to cooling hours, so the same upgrade is worth more in Phoenix than in Seattle. The tonnage stays fixed either way, which is why a quote that swaps 3 tons for 2.5 tons to hit an efficiency target is solving the wrong problem.

Sizing mistakes that turn a ton answer into a wrong quote

Dividing by 1,000. This is the classic slip: 36,000 ÷ 1,000 = 36 is not 36 tons, it is 36 kBtu per hour. A quote built on that figure oversizes the job twelve times over.

Confusing the two tons. A ton of weight is 2,000 pounds. A ton of cooling is 12,000 BTU/h. Nothing about a 3 ton condenser weighs 6,000 pounds.

Oversizing on purpose. A unit one size too large cools the air before it pulls the humidity out, so the rooms feel clammy and the compressor short cycles. The 20 to 30 BTU/h range already carries a margin.

Trusting a nominal rating at any outdoor temperature. Capacity on the nameplate is measured at 95°F outdoor air. A 3 ton unit at 105°F delivers less than 36,000 BTU/h, and the derate sits in the manufacturer's expanded ratings.

Copying the old unit. Replacing 3 tons with 3 tons repeats a sizing decision made in 1998, before the windows and the insulation changed.

Where the conversion shows up in a real quote

Quotes and invoices rarely use the same unit. A contractor quotes 3.5 tons, the permit lists 42,000 BTU/h, and the spec sheet shows 12.31 kW of cooling. All three describe one machine: 3.5 × 12,000 = 42,000, and 42,000 × 0.00029307107 = 12.31 kW.

Mini splits are sold in single steps of 9,000 BTU/h, so four zones of 9,000 BTU/h add to 36,000 BTU/h, or 3 tons of capacity in total. A portable unit marked 8,000 BTU/h is 8,000 ÷ 12,000 = 0.6667 ton, and its real capacity drops once the exhaust hose heats the room back up.

Heating equipment uses BTU/h as well, and that is where the two trades meet. A 60,000 BTU/h furnace and a 5 ton air conditioner both carry the number 60,000, but only one of them is 5 tons. When a figure looks too large for the house, check which side of the system it belongs to before dividing.