Estimate the cooling capacity required for your room based on dimensions and environmental factors.
Excellent (New construction, high R-value)
Average (Standard modern windows/walls)
Poor (Older home, drafty windows)
Heavily Shaded
Normal Exposure
Very Sunny (Lots of windows)
Recommended Cooling Capacity:0 BTU(Equivalent to 0 Tons)
*This is an estimate. Always consult a licensed HVAC professional before purchasing equipment.
How to Calculate BTU for Your Room
Choosing the right size air conditioner or heater is critical for both comfort and energy efficiency. An undersized unit will run constantly without cooling the space, while an oversized unit will cycle on and off too frequently, leading to poor dehumidification and increased wear and tear.
BTU stands for British Thermal Unit. It is a measure of heat energy. In the context of HVAC, it represents how much heat an air conditioner can remove from a room per hour. The general rule of thumb is that you need roughly 20 BTUs for every square foot of living space.
The HVAC Sizing Formula
Our calculator uses a refined version of the standard square footage formula to provide a more accurate estimate. The core calculation is:
Step 1: Square Footage = Width × Length
Step 2: Base BTU = Square Footage × 20
Step 3: Adjust for Sun & Insulation (Multipliers range from 0.9 to 1.2)
Step 4: Account for People (Add 600 BTUs for every person beyond the first two)
BTU Sizing Chart
Area (Sq. Ft.)
Capacity Needed (BTU/hr)
100 to 150
5,000
150 to 250
6,000
250 to 350
8,000
350 to 450
10,000
450 to 550
12,000
550 to 700
14,000
700 to 1,000
18,000
Frequently Asked Questions
What is "Tonnage" in HVAC?
Tonnage refers to the cooling capacity of the unit. One ton of cooling is equivalent to 12,000 BTUs per hour. If our calculator suggests 24,000 BTUs, you need a 2-ton unit.
What happens if I buy a unit that is too large?
A unit that is too powerful for the space will reach the thermostat setting too quickly. This "short-cycling" prevents the unit from properly removing humidity, leaving the air feeling cold but "clammy" or damp.
function calculateBTU() {
var width = parseFloat(document.getElementById("roomWidth").value);
var length = parseFloat(document.getElementById("roomLength").value);
var insulation = parseFloat(document.getElementById("insulationQuality").value);
var sun = parseFloat(document.getElementById("sunExposure").value);
var occupants = parseInt(document.getElementById("occupants").value);
if (isNaN(width) || isNaN(length) || width <= 0 || length 2) {
adjustedBTU += (occupants – 2) * 600;
}
// Tonnage calculation (12,000 BTU = 1 Ton)
var tonnage = (adjustedBTU / 12000).toFixed(2);
// Display results
document.getElementById("hvac-result").style.display = "block";
document.getElementById("btuValue").innerText = Math.round(adjustedBTU).toLocaleString() + " BTU";
document.getElementById("tonnageValue").innerText = "(Equivalent to " + tonnage + " Tons)";
// Scroll to result smoothly
document.getElementById("hvac-result").scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}