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Good (Standard)
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Recommended Cooling Capacity
0 BTU
(0.0 Tons)
How to Calculate BTU for Your Room
Choosing the right size air conditioner is critical for both comfort and energy efficiency. An air conditioner's capacity is measured in British Thermal Units (BTUs). If the unit is too small, it won't cool the room effectively during peak heat. If it is too large, it will cycle on and off too quickly, failing to remove humidity and causing unnecessary wear on the parts.
The BTU Formula Used
This calculator uses the industry standard base formula while adjusting for specific environmental variables:
Base Calculation: Area (Length × Width) × 20.
Occupancy: If more than two people regularly occupy the room, add 600 BTUs for each additional person.
Kitchens: If the unit is installed in a kitchen, the capacity should be increased by 4,000 BTUs to account for heat generated by appliances.
Sunlight: Heavily shaded rooms need 10% less capacity, while very sunny rooms need 10% more.
Common Area Estimates
Area (Sq. Ft.)
Capacity Needed (BTU)
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
Real-World Example
Suppose you have a 15′ x 20′ living room (300 sq. ft.) that is very sunny, used by 3 people, and is not a kitchen.
1. Base: 300 sq. ft. × 20 = 6,000 BTUs.
2. Sunlight: 6,000 × 1.1 (sunny) = 6,600 BTUs.
3. People: Add 600 BTUs for the 3rd person = 7,200 BTUs total.
function calculateBTU() {
var length = parseFloat(document.getElementById('roomLength').value);
var width = parseFloat(document.getElementById('roomWidth').value);
var sun = parseFloat(document.getElementById('sunExposure').value);
var occupants = parseInt(document.getElementById('occupants').value);
var kitchenExtra = parseFloat(document.getElementById('isKitchen').value);
var insulation = parseFloat(document.getElementById('insulation').value);
if (isNaN(length) || isNaN(width) || length <= 0 || width 2) {
totalBTU += (occupants – 2) * 600;
}
// Rounding
var finalBTU = Math.round(totalBTU);
var tons = (finalBTU / 12000).toFixed(2);
// Display
document.getElementById('btuResult').style.display = 'block';
document.getElementById('btuDisplay').innerText = finalBTU.toLocaleString() + " BTU/hr";
document.getElementById('tonnageDisplay').innerText = "(" + tons + " Tons)";
var note = "For a " + area.toFixed(0) + " sq. ft. room, we recommend a unit with at least " + finalBTU.toLocaleString() + " BTUs. ";
if (finalBTU > 24000) {
note += "For this size, consider a central AC system or a large split-system unit.";
} else {
note += "A standard window unit or mini-split should be sufficient for this space.";
}
document.getElementById('resultNote').innerText = note;
}