BTU Calculator
Find the right AC or heater BTU for any room. Accounts for sunlight, occupants, kitchen heat, insulation, and climate zone. Includes BTU converter and energy cost estimator.
5,500
BTU/HR
0.46
TONS
1.61
KW
❄️ AC / Cooling BTU Calculator
Find the right BTU rating for an air conditioner based on room size and conditions.
BTU Needed (Cooling)
5,500
BTU/hr
250 sq ft room
Tons
0.46 tons
Kilowatts
1.61 kW
5,500
BTU/hr
0.46
Tons
1.612
kW
1,612 W
Watts
AC Sizing — 250 sq ft Room
AC Unit Recommendations
Window AC
5,000-25,000 BTU range
Portable AC
8,000-14,000 BTU range
Mini-Split
6,000-36,000 BTU range
Central AC
18,000-60,000 BTU range
Room Analysis
5,000
Base BTU
None
Ceiling Adj.
1x
Climate Factor
1x
Insulation Factor
5,500
Adjusted BTU
0.46
Tons
1.61 kW
Kilowatts
2,000 ft³
Room Volume
Understanding BTUs for Heating & Cooling
A BTU (British Thermal Unit) is the amount of energy needed to raise one pound of water by one degree Fahrenheit. In HVAC, BTU/hr measures how fast a unit can move heat into or out of a space — and one ton of cooling capacity, a term you'll see on central AC nameplates, always equals exactly 12,000 BTU/hr. Getting the sizing right matters in both directions: too few BTUs and a unit runs constantly without keeping up, too many and it short-cycles without properly controlling humidity.
📎 BTU Quick Reference
Room sizing (cooling): ~20 BTU/hr per sq ft (basic) Small room (150 sq ft): 5,000-6,000 BTU | Medium room (350 sq ft): 8,000-10,000 BTU Large room (550 sq ft): 12,000-14,000 BTU | Open plan (1,000 sq ft): 18,000-21,000 BTU Conversions: 1 ton = 12,000 BTU/hr | 1 kW = 3,412 BTU/hr | 1 BTU/hr = 0.2931 Watts Energy cost formula: Watts = BTU/hr ÷ EER | Daily kWh = Watts × hours ÷ 1000 | Monthly cost = daily kWh × 30 × $/kWh