BTU Calculator
Calculate the required BTU for heating and cooling a room. Properly size your air conditioner or furnace based on room dimensions and conditions.
Room Dimensions
Room Conditions
Windows & Doors
Cooling Required
Heating Required
Room Summary
AC Unit Size Recommendation
BTU Reference by Room Size
| Room Size (sq ft) | Cooling BTU | Heating BTU |
|---|---|---|
| 100-200 | 5,000-6,000 | 4,000-8,000 |
| 200-300 | 6,000-7,000 | 8,000-12,000 |
| 300-400 | 7,000-9,000 | 12,000-18,000 |
| 400-500 | 9,000-11,000 | 18,000-22,000 |
| 500-700 | 11,000-14,000 | 22,000-28,000 |
| 700-1000 | 14,000-18,000 | 28,000-36,000 |
BTU Calculation Factors
- Base BTU: 25-30 BTU per sq ft
- Ceiling height: Add 10% for high ceilings
- Windows: +10% per large window
- Sun exposure: +10-20% for sunny rooms
- Occupants: +600 BTU per person
- Kitchen: +4,000 BTU
Common BTU Values
- 5,000 BTU: Small bedroom (100-150 sq ft)
- 8,000 BTU: Medium room (200-300 sq ft)
- 12,000 BTU: Large room (400-500 sq ft)
- 18,000 BTU: Open concept (600-800 sq ft)
- 24,000 BTU: Small apartment (800-1000 sq ft)
Frequently Asked Questions
What is BTU?
BTU (British Thermal Unit) is a unit of energy used to measure heating and cooling capacity. One BTU is the amount of energy needed to raise one pound of water by one degree Fahrenheit. For HVAC, BTU ratings indicate how much heat an AC can remove or a heater can produce per hour.
How do you calculate BTU for a room?
Step 1: Calculate room area (length × width)
Step 2: Multiply by 25-30 BTU per sq ft (base)
Step 3: Adjust for ceiling height (+10% per ft over 8')
Step 4: Add for windows, occupants, sun exposure
Step 5: Add 4,000 BTU for kitchens
What size AC do I need for a 300 sq ft room?
A 300 sq ft room typically needs 7,000-9,000 BTU for cooling. Our calculator provides an exact recommendation based on your specific room conditions (windows, sun exposure, insulation, etc.).
What happens if BTU is too high or too low?
Too low: Unit runs constantly, can't reach desired temperature, higher energy bills, reduced lifespan.
Too high: Short cycling (turns on/off frequently), poor humidity control, uncomfortable temperature swings, wasted energy.
How many BTU per square foot?
General guidelines:
- Cooling: 20-30 BTU per sq ft
- Heating: 25-40 BTU per sq ft (varies by climate)
- Poor insulation: Use higher end of range
- Good insulation: Use lower end of range
Does ceiling height affect BTU requirements?
Yes! Standard BTU calculations assume 8-foot ceilings. For taller ceilings, add 10-15% BTU for each additional foot of height. Our calculator automatically adjusts for ceiling height.