Air Conditioner BTU Calculator

Find the perfect AC size for your room in seconds

Room Length (feet)

Room Width (feet)

Ceiling Height

Number of People

Sun Exposure

Shaded

Average

Very Sunny

Room Type

Bedroom

Kitchen

Living Room

Recommended AC Capacity

BTU per hour

Calculation Breakdown

Room Area: 0 sq ft

Base BTU (20 BTU/sq ft): 0

Ceiling Adjustment: 0

Sun Exposure Adjustment: 0

Occupancy Adjustment: 0

Room Type Adjustment: 0

Shopping Guidance:

How to Use This BTU Calculator

This calculator helps you determine the correct air conditioner size for your room based on multiple factors that affect cooling efficiency:

Measure your room: Enter the length and width in feet. The calculator will compute the square footage automatically.
Select ceiling height: Higher ceilings require more cooling capacity.
Count occupants: Each person adds about 600 BTU of heat.
Assess sun exposure: South-facing or west-facing rooms get hotter and need more cooling.
Choose room type: Kitchens generate extra heat from appliances.

Example: A 15×12 bedroom (180 sq ft) with standard ceilings, average sun exposure, and 2 people needs approximately 5,000 BTU. A similarly sized kitchen with high sun exposure would need closer to 6,500 BTU.

Understanding the Calculation

The calculator uses the industry standard of 20 BTU per square foot as a baseline, then adjusts for:

Ceiling height: High ceilings add 10%, vaulted ceilings add 20%
Sun exposure: Shaded rooms reduce by 10%, very sunny rooms add 10%
Occupancy: 600 BTU added per person beyond the first two
Room type: Kitchens add 4,000 BTU for heat-generating appliances

Common AC Unit Sizes

Window and portable air conditioners typically come in these BTU ratings:

5,000 BTU: 100-150 sq ft (small bedroom, office)
6,000 BTU: 150-250 sq ft (bedroom, den)
8,000 BTU: 250-350 sq ft (master bedroom, large office)
10,000 BTU: 350-450 sq ft (studio apartment, large bedroom)
12,000 BTU: 450-550 sq ft (apartment, small house room)
14,000 BTU: 550-700 sq ft (large living room)

Why Correct BTU Sizing Matters

Undersized Unit Problems

Runs constantly, driving up energy bills
Never reaches desired temperature
Wears out faster from overwork
Cannot remove humidity effectively

Oversized Unit Problems

Short-cycles (turns on and off frequently)
Doesn't run long enough to dehumidify
Room feels clammy and uncomfortable
Uses more energy than necessary
Costs more upfront

Tips for Maximum Efficiency

Seal gaps around windows and doors
Use curtains or blinds to block direct sunlight
Ensure proper insulation in walls and ceiling
Clean or replace air filters monthly
Keep the unit at least 20 inches from walls for airflow
Use a programmable thermostat or timer

Frequently Asked Questions

What does BTU stand for?

BTU stands for British Thermal Unit. It's the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. In air conditioning, it measures how much heat the unit can remove from a room per hour.

Should I round up or down when choosing an AC unit?

If you're between sizes, it's generally better to go slightly larger rather than smaller, but avoid oversizing by more than 15%. An AC that's too large will cycle on and off too frequently and won't dehumidify properly.

Does climate affect BTU requirements?

Yes. This calculator uses standard assumptions for moderate climates. If you live in an extremely hot climate (consistent 95°F+ summers), consider adding 10-20% to the recommended BTU. In milder climates, you might reduce by 10%.

Can I use one AC unit to cool multiple rooms?

Not effectively. Air conditioners work best when cooling a single enclosed space. For multiple rooms, calculate BTU for each room separately or consider a multi-zone mini-split system.

How much does it cost to run an air conditioner?

A 10,000 BTU unit running 8 hours per day typically costs $25-40 per month, depending on your electricity rate. Higher efficiency units (higher EER ratings) cost less to operate.

What's the difference between BTU and EER?

BTU measures cooling capacity (how much heat is removed), while EER (Energy Efficiency Ratio) measures efficiency (BTU per watt of electricity). A higher EER means lower operating costs for the same cooling power.