Determine the exact BTU capacity needed for your air conditioner.
Heavily Shaded (-10%)
Normal Exposure
Very Sunny (+10%)
Standard Bedroom / Good Insulation
Kitchen (+4,000 BTU)
Living Room / Average Insulation
Converted Attic / Poor Insulation
Recommended Cooling Capacity
0
BTUs per hour (BTU/hr)
How to Calculate Cooling Load (BTU) for Your Space
Selecting the right air conditioner is more than just picking a brand; it's about matching the cooling capacity (measured in British Thermal Units or BTUs) to the physical characteristics of your room. An undersized unit will run constantly without cooling the room, while an oversized unit will cycle on and off too frequently, failing to dehumidify the air properly.
Factors That Influence Your BTU Needs
While square footage is the primary factor, several environmental variables play a crucial role in how much heat your AC needs to remove:
Room Dimensions: The total area (Length x Width) determines the base cooling load.
Occupancy: Humans generate heat. We calculate an additional 600 BTUs for every person beyond the first two occupants.
Sunlight: A room with large, south-facing windows in a sunny climate requires about 10% more cooling power. Conversely, a heavily shaded room can reduce the load by 10%.
Kitchen Factor: If you are cooling a kitchen, the heat generated by ovens, stoves, and refrigerators requires a massive jump—usually an additional 4,000 BTUs.
Insulation: Poorly insulated spaces like attics or old garages lose cool air quickly and absorb heat faster, requiring higher capacity units.
Standard BTU Chart for Room Sizes
Area (Sq. Ft.)
Base Capacity (BTU/hr)
100 to 150
5,000
150 to 250
6,000
250 to 350
7,000 to 8,000
400 to 450
10,000
550 to 700
14,000
1,000 to 1,200
21,000
Understanding AC Tonnage
In residential HVAC systems, you might hear the term "tonnage." One ton of cooling is equivalent to 12,000 BTUs per hour. This unit of measurement dates back to the days when ice was used for cooling; one ton represents the cooling power required to melt one ton of ice over a 24-hour period. Our calculator provides both the BTU requirement and the equivalent tonnage to help you talk to contractors.
function calculateCoolingLoad() {
// Get Input Values
var length = parseFloat(document.getElementById('roomLength').value);
var width = parseFloat(document.getElementById('roomWidth').value);
var occupants = parseInt(document.getElementById('occupants').value);
var sun = document.getElementById('sunExposure').value;
var roomType = document.getElementById('roomType').value;
var windows = parseInt(document.getElementById('windowCount').value);
// Validate inputs
if (isNaN(length) || isNaN(width) || length <= 0 || width 2) {
occupantAdjustment = (occupants – 2) * 600;
}
// 4. Adjust for Windows
// Simple estimation: 100 BTU per window
var windowAdjustment = windows * 100;
// Sum initial calculations
var subTotal = baseBTU + typeAdjustment + occupantAdjustment + windowAdjustment;
// 5. Sun Exposure Multiplier
var finalBTU = subTotal;
if (sun === "shaded") {
finalBTU = subTotal * 0.90;
} else if (sun === "sunny") {
finalBTU = subTotal * 1.10;
}
// Round the result
var resultBTU = Math.round(finalBTU);
var tonnage = (resultBTU / 12000).toFixed(2);
// Display Result
document.getElementById('btuValue').innerHTML = resultBTU.toLocaleString();
document.getElementById('tonnageValue').innerHTML = "Estimated AC Tonnage: " + tonnage + " Tons";
document.getElementById('coolResult').style.display = 'block';
// Smooth scroll to result
document.getElementById('coolResult').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}