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Free BTU Calculator
Estimate the cooling capacity in BTU per hour needed for a room.
What is the BTU Calculator?
Estimate the cooling capacity in BTU per hour needed for a room.
It starts with 20 BTU/h per square foot scaled by ceiling height over 8 feet, then multiplies by climate and sun exposure factors. 600 BTU/h is added for each person beyond two and 4,000 for a kitchen, and the total is also shown in kilowatts and tons.
Home and building jobs are easier to price when you know how much material you really need. A quick estimate also helps you avoid buying too little or too much.
How to use the BTU Calculator
Using the btu calculator takes a minute or two. Your entries are saved in this browser, so you can come back later and carry on.
Step 1
Enter the measurements of the area you are working on.
Step 2
Read the amount of material needed, including a waste allowance where relevant.
Step 3
Round up when you buy, and check the figures with your supplier.
Tips for better results
This is a rule of thumb, not a full load calculation, so an oversized unit can cycle too often. For whole-house or ducted systems have an HVAC professional perform a proper load calculation and follow local codes.
Add 5 to 10 percent for waste, cuts and mistakes.
Measure twice, order once, and check quantities with your supplier.
Privacy and where your data goes
Everything you type into the btu calculator stays on your own device. Zapxa does not receive your numbers or documents. If you clear your browser data, your saved entries will be removed, so download a PDF of anything you want to keep.
Frequently asked questions
How many BTUs per square foot do I need?
This calculator starts at 20 BTU/h per square foot for an 8 ft ceiling, then adjusts for climate, sun, occupants and kitchens.
How many BTUs are in a ton of cooling?
One ton of cooling equals 12,000 BTU/h, which the calculator uses to show the result in tons.
Is the btu calculator free?
Yes. It is free to use with no signup, no watermark and no usage limits.
Is my data private?
Yes. Your inputs are processed in your browser and saved only in its local storage. They are not uploaded to our servers.
Does it work on mobile?
Yes. Zapxa works on phones, tablets and desktops. Use the print button or download a PDF to keep a copy.
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