BTU Per Square Foot Chart - Complete AC Sizing Guide

Use our comprehensive BTU per square foot chart to determine the right size air conditioner for any room. This guide includes adjustments for various room conditions and usage scenarios.

Quick Reference BTU Chart

Square Footage Base BTU Requirement With Sunny Exposure With Shade
100-150 5,000 5,500 4,500
150-250 6,000 6,600 5,400
250-300 7,000 7,700 6,300
300-350 8,000 8,800 7,200
350-400 9,000 9,900 8,100
400-450 10,000 11,000 9,000
450-550 12,000 13,200 10,800
550-700 14,000 15,400 12,600
700-1000 18,000 19,800 16,200
1000-1200 21,000 23,100 18,900
1200-1400 23,000 25,300 20,700

Basic BTU Calculation Formula

For a basic estimation, use this formula:

  • Base BTU = Square Footage × 20
  • Sunny rooms: Add 10% to base BTU
  • Shaded rooms: Subtract 10% from base BTU
  • Kitchens: Add 4,000 BTU to base calculation

Room-Specific BTU Requirements

Room Type BTU per Square Foot Additional Factors
Living Room 20 +10% for high ceiling
Bedroom 18 -5% for night use
Kitchen 25 +4,000 BTU base addition
Home Office 22 +1,000 BTU per computer
Sunroom 28 +15% for glass exposure

Adjustment Factors

Ceiling Height Adjustments

  • 8 ft (standard): No adjustment
  • 9 ft: Add 10% to base BTU
  • 10 ft: Add 15% to base BTU
  • 12 ft or higher: Add 25% to base BTU

Window Exposure Adjustments

  • Northern exposure: -5% from base BTU
  • Eastern exposure: No adjustment
  • Southern exposure: +10% to base BTU
  • Western exposure: +15% to base BTU

Occupancy Adjustments

  • Add 600 BTU per person over 2 people
  • Add 500 BTU for each high-heat appliance
  • Subtract 10% for rarely used rooms
  • Add 15% for frequently used rooms

Special Considerations

Insulation Quality

  • Well-insulated: Use base BTU calculation
  • Poorly insulated: Add 20% to base BTU
  • No insulation: Add 30% to base BTU

Room Location

  • Ground floor: Use base BTU calculation
  • Upper floor: Add 10% to base BTU
  • Basement: Subtract 10% from base BTU

Frequently Asked Questions About BTU Per Square Foot

How many BTUs do I need per square foot?

As a general rule, you need about 20 BTUs per square foot of living space. However, this is just a baseline - factors like sun exposure, ceiling height, and room usage can affect this number. For example:

  • Sunny rooms need about 22-23 BTUs per square foot
  • Shaded rooms might only need 18-19 BTUs per square foot
  • Kitchens often need 25-30 BTUs per square foot due to appliance heat

Why is my BTU calculation different from standard charts?

Your calculation might differ because of specific room conditions such as:

  • Higher or lower ceiling height than the standard 8 feet
  • Number of windows and their exposure to sunlight
  • Quality of insulation
  • Number of people regularly in the room
  • Heat-generating appliances

Should I always round up to the next BTU size?

Not necessarily. While it's better to slightly oversize than undersize, going too large can cause problems. Stay within 10-15% of your calculated BTU need. If your calculation falls between available sizes, consider factors like:

  • Climate zone (humid areas benefit from slight oversizing)
  • Room usage patterns
  • Future needs
  • Energy efficiency goals

How do I calculate BTUs for an open floor plan?

For open floor plans:

  1. Calculate the total square footage of the connected space
  2. Use the standard 20 BTU per square foot as a starting point
  3. Add adjustments for kitchen areas (+4,000 BTU)
  4. Consider the highest sun exposure of any area
  5. Account for the highest ceiling in the space

Do I need to adjust BTUs for different climates?

Yes, climate affects BTU requirements:

  • Hot, humid climates: Add 10-15% to base calculation
  • Hot, dry climates: Add 5-10% to base calculation
  • Moderate climates: Use standard calculation
  • Cool climates: Reduce by 5-10% from base calculation

How do windows affect BTU requirements?

Windows can significantly impact cooling needs:

  • Large windows facing south: Add 10-15% to BTU calculation
  • Double-pane windows: Standard calculation
  • Single-pane windows: Add 10% to calculation
  • Energy-efficient windows: Reduce by 5%
  • Window treatments can help reduce requirements

Should I include hallways in square footage calculations?

For BTU calculations:

  • Include hallways if they're part of the cooled space
  • Use 50% of hallway square footage if rarely occupied
  • Consider air flow patterns in your home
  • Account for heat from adjacent rooms

How often should I revise my BTU calculations?

Review your BTU requirements when:

  • Renovating or changing room purpose
  • Adding or removing heat-generating equipment
  • Upgrading windows or insulation
  • Experiencing consistent cooling issues
  • Changes in room occupancy patterns

What's the impact of ceiling height on BTU calculations?

Ceiling height affects cooling requirements significantly:

  • 8 ft (standard): Base calculation
  • 9 ft: Add 10% to base BTU
  • 10 ft: Add 15% to base BTU
  • 12 ft or higher: Add 25% to base BTU
  • Cathedral ceilings may require additional adjustments

Can I use the same BTU calculation for different seasons?

Your BTU needs might vary seasonally:

  • Summer peak demands are typically highest
  • Spring/Fall might need 10-15% less capacity
  • Consider a unit with variable capacity
  • Factor in humidity control needs
  • Account for seasonal occupancy changes