AC Tonnage Calculator
Estimate the BTU and tonnage of air conditioning a room needs, adjusted for occupants, sun, and kitchen load.
❄️ What is the AC Tonnage Calculator?
The AC tonnage calculator estimates how much cooling capacity a room needs, expressed in BTUs per hour and in tons, so you can choose the right size air conditioner. It starts from the floor area and then adjusts for the things that add heat: the number of people, how much sun the room gets, and whether it is a kitchen.
Sizing is the decision that makes or breaks comfort and running cost. Shoppers use it to pick between a 1 ton and a 1.5 ton unit, landlords use it to spec cooling for a rental, and anyone replacing an old air conditioner uses it to check whether the previous size was actually right. Because air conditioners are sold in fixed sizes such as 0.75, 1, 1.5, and 2 tons, the goal is to land on the load and round to the nearest sensible unit.
A widespread misconception is that a bigger air conditioner is always better. In reality an oversized unit cools the air so fast that it switches off before it has pulled enough moisture out, leaving the room cold but damp, and the constant short cycling wastes electricity and wears out the compressor. An undersized unit, on the other hand, runs non-stop on hot days and never quite catches up. The right size, matched to the room, runs steadily and efficiently.
This tool is useful because it turns a room into a defensible BTU and tonnage figure using the standard rule-of-thumb load method, with adjustments for the factors that matter most, and it shows the working so you can see how each part of the room contributes to the total.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Bedroom, 400 sq ft, average sun
Example 2 - Sunny living room, 600 sq ft, 4 people
Example 3 - Kitchen, 300 sq ft, 3 people
❓ Frequently Asked Questions
🔗 Related Calculators
What size air conditioner do I need for a room?
Start with about 20 BTU per hour per square foot, then adjust. A 400 square foot room needs roughly 8,000 BTU, about two-thirds of a ton, so a 1 ton unit is a safe choice. Add capacity for extra occupants, strong sun, or a kitchen.
How many BTU are in a ton of air conditioning?
One ton equals 12,000 BTU per hour. The term comes from the cooling power of a ton of ice melting over 24 hours. So a 24,000 BTU unit is 2 tons, and an 18,000 BTU unit is 1.5 tons. This calculator reports both BTU and tons.
How do you calculate AC tonnage from room size?
Multiply the floor area in square feet by 20 BTU to get the base load, apply a sun-exposure factor, add 600 BTU for each occupant over two, and add 4,000 BTU for a kitchen. Divide the total BTU by 12,000 to get tons. A 400 square foot average room works out to about 0.67 tons.
Is it bad to oversize an air conditioner?
Yes. An oversized unit cools the air quickly but shuts off before it removes enough humidity, leaving the room cold and clammy, and the frequent on-off cycling wastes energy and shortens the compressor's life. Matching capacity to the room gives steady, efficient, comfortable cooling.
Does sun exposure change the AC size I need?
Yes. A room with large west or south-facing windows gains significant solar heat and needs more cooling than a shaded room of the same size. This calculator applies about a 10 percent increase for a sunny room and a 10 percent reduction for a heavily shaded one.
How much extra cooling does a kitchen need?
Add around 4,000 BTU per hour for a kitchen, because ovens, stoves, and refrigerators release a lot of heat. This calculator includes that allowance when you mark the room as a kitchen, on top of the area and occupant loads.
How many BTU do I need per square foot?
About 20 BTU per hour per square foot is the common rule of thumb for a standard room with 8 foot ceilings. Very sunny rooms, high ceilings, and heat-generating spaces need more, while well-insulated, shaded rooms need a little less. This calculator starts from 20 and adjusts.
What is the difference between a 1 ton and 1.5 ton AC?
A 1 ton unit provides 12,000 BTU per hour and a 1.5 ton unit provides 18,000 BTU, so the larger unit cools about 50 percent more area or a hotter, sunnier room. Choose based on the calculated BTU load rather than guessing, and round up to the next standard size.
How accurate is a BTU rule-of-thumb estimate?
It gives a solid starting point, usually within 10 to 20 percent of a detailed Manual J load calculation. Factors like insulation quality, ceiling height, window type, and climate affect the true load. For a large or unusual space, have an HVAC professional run a full assessment.
Does ceiling height affect air conditioner size?
Yes. Cooling load depends on room volume, so a room with 10 or 12 foot ceilings needs more capacity than the same floor area with 8 foot ceilings. This calculator assumes standard 8 foot ceilings, so add roughly 10 to 25 percent for noticeably higher ceilings.