"One ton per 500 square feet" gets you close, then climate, insulation, and sun pull the real number up or down. This tool adjusts for all of it and snaps the result to a size you can actually buy. It is a fast estimate to sanity-check a quote, not a replacement for a full Manual J. Runs in your browser; nothing is uploaded.
A ton is not weight, it is capacity: 12,000 BTU per hour of heat the system can remove, the amount it takes to melt a ton of ice in a day. So a 3 ton AC moves 36,000 BTU/hr. Sizing the equipment means estimating how much heat your space gains on a design day, then matching a unit to it. Square footage is the biggest single driver, which is why per-square-foot rules get you in the neighborhood, but climate, insulation, and sun decide whether you land at the low or high end of the range.
Residential condensers come in half-ton steps, 1.5 through 5 tons, with no 4.5 ton unit in most lines. A raw calculation might say 3.7 tons, but you will install a 3.5 or a 4. This tool shows both the raw number and the real size so you can see how close the call is, and when the honest answer is "either could work, and the load calc decides."
Rounding up is the most expensive instinct in residential HVAC. An oversized system satisfies the thermostat on temperature before it runs long enough to pull humidity out of the air, so the house feels cold and damp and the compressor short-cycles itself to an early failure. Right-sizing means longer, gentler run times that actually dehumidify and use less energy. That is why the trade sizes off a load calculation instead of a tape measure.
Once the size is settled, the job still has to be quoted, won, and billed. Present the replacement as a clean estimate with the equipment and reasoning spelled out and you become the contractor the homeowner trusts over two cheaper business cards. FieldForge turns that into a spoken sentence: say the scope and the estimate or invoice builds from your price book, captures the model and serial for the warranty record, and texts a payment link the moment the system is running. Need a quick document today? Use the free HVAC invoice generator.
Roughly 500 to 600 in a mixed climate, less in the hot humid South, more in cool dry regions. The calculator adjusts that base for your specifics.
Often around 3 to 4 tons in a mixed climate, but insulation, windows, and air sealing move it. Estimate above, then confirm with a Manual J.
No. It is a fast rule-of-thumb check. A full ACCA Manual J should size the equipment you actually install.