HVAC Load & AC Tonnage Calculator
Work out the HVAC cooling load and AC tonnage a room needs — in tons, BTU/hr and kW — from its size in sq ft (m²), sun exposure, insulation, occupants and equipment. Then see the standard air conditioner size that covers it. Everything runs on your device.
Guide: How Many BTU Do I Need to Cool a Room?Your room
Conditions & heat sources
Load breakdown (BTU/hr)
A sizing guide, not a heat-load study
Figures use a rule of thumb of about 600 BTU/hr per m², adjusted for your conditions. A formal calculation accounts for window sizes and orientation, wall construction, air leakage and local climate — get one done for unusual spaces like glass-walled rooms, server rooms or halls.
Questions & answers
Everything you need to understand the hvac load & ac tonnage calculator.
What does this HVAC load calculator do?
It estimates the cooling capacity an air conditioner needs to keep a room comfortable — in BTU/hr, tons and kW. Enter the room size in sq ft (m²), how much sun it gets, the insulation quality and what generates heat inside, and it returns the load plus the next standard AC size that covers it.
How is the cooling load calculated?
It starts from a rule of thumb of about 20 BTU/hr per square foot of floor (≈600 BTU/hr per m²) at a standard 8 ft (2.4 m) ceiling, scaled for taller rooms. That base is adjusted for sun exposure and insulation, then heat sources are added on top: roughly 600 BTU/hr per occupant beyond two, about 4,000 BTU/hr for a kitchen, and 3.4 BTU/hr for every watt of equipment running in the room.
How many BTU per square foot do I need?
Most rooms fall between 15 and 25 BTU/hr per square foot (about 500–750 BTU/hr per m²). A shaded, well-insulated bedroom sits at the low end; a sunny, poorly insulated living area with people and electronics at the high end. That is why the calculator asks about sun, insulation and heat sources rather than using one flat figure.
How do I convert BTU to kW?
Divide by about 3,412: a 12,000 BTU/hr unit delivers roughly 3.5 kW of cooling — which is also 1 ton, since 1 ton = 12,000 BTU/hr. Note that is cooling output, not electrical draw — an air conditioner moves more heat than the electricity it consumes, typically 3 or more kW of cooling per kW of input.
What size air conditioner should I buy?
Round up to the next standard size — units typically come in 9,000 (¾ ton), 12,000 (1 ton), 18,000 (1.5 ton) and 24,000 BTU/hr (2 ton) and up, and the calculator suggests the size for you. Slightly bigger is fine, but heavily oversized units short-cycle: they cool the air fast without dehumidifying properly, leaving the room cold and clammy while wearing the compressor.
How accurate is this estimate?
It is a sizing guide, not a full heat-load study. A formal calculation (such as Manual J or CIBSE methods) accounts for window sizes and orientation, wall construction, air leakage and local climate. For a typical room the rule of thumb lands close, but for unusual spaces — glass walls, server rooms, halls — have a full calculation done.
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