BTU Calculator
A rule-of-thumb cooling load — not Manual J. Click any i for detail.
Space
Area (sq ft)
i
Area
Conditioned floor area. |
|
|---|---|
BTU per sq ft
i
Climate factor
Hot-humid ~25; mixed ~20; mild ~18. |
|
People
i
Occupants
First two included in the base; each extra adds ~600 BTU. |
|
Kitchen
i
Kitchen
Adds a 4,000 BTU sketch for cooking load. |
|
Very sunny
i
Sun
Adds ~2 BTU per sq ft for heavy west/south glass. |
How to use this calculator
- Enter floor area.
- Raise the factor in a hot climate.
- Add people, kitchen, and sun if they apply.
- Convert to tons at 12,000 BTU = 1 ton.
Results explained
Headline is a rounded BTU/hr sketch. Mini-splits and central AC are sold in tons. For a ductless head count, see mini-split sizing.
Quick reference: BTU
Oversizing causes short-cycling; undersizing never catches up on the hottest day.
| Item | Detail |
|---|---|
| 1 ton | 12,000 BTU/hr |
| Mixed climate factor | ~20 BTU/sq ft |
| Extra person | ~600 BTU/hr |
| Kitchen adder | ~4,000 BTU/hr |
Insulation, windows, and infiltration dominate real loads.
How the estimate is built
BTU ≈ area × factor + max(0, people−2)×600 + kitchen + sun. Tons = BTU / 12,000.
Example scenario
400 sq ft × 20 = 8,000 BTU (~0.67 tons) before extras.
FAQ
Is this Manual J?
No. Manual J uses construction, windows, and design temperatures.
Heating BTU?
Heating is a different load (often higher in cold climates). This page is cooling-oriented.
Mini-split size chart?
Use the mini-split sizing calculator for heads + insulation.