BTU Heat Calculator Online

You need accuracy to ensure your heating, ventilation, and air conditioning (HVAC) systems work properly in your home or office. You might use math formulas to determine the amount of energy needed to warm or cool your rooms. However, using our BTU heat calculator and BTU converter is way easier.

BTU Calculator


Please fill in any 2 of the below fields and click "Calculate". The resulted value will appear in the blank field.


BTU Converter


Please fill any of the below fields and click "Convert" to calculate others.


What Is BTU?

The BTU (British Thermal Unit) is a unit of measurement for thermal energy. It shows how much heat you need to increase the temperature of one pound (0,453 kilograms) of liquid water by 1 degree Fahrenheit. A single BTU is quite a small amount of energy — it equals roughly the same power released by a burning match.

BTUs have different uses, depending on the industry. They are primarily used for choosing HVAC equipment. The labels on technical equipment show the heating capacity of appliances (a higher rating equals greater heating capacity). Given that you know your room's precise measurement, you can determine the optimal AC unit or garage heater (BTU calculator makes calculations easier, though) for any room.

The Energy Information Administration also uses BTUs for fuels. It’s possible to convert the energy sources produced by fuel into BTU for comparing different types of gasses and oils.

How to Calculate BTU?

Calculating BTU isn’t hard if you know the formulas, but you still have to measure your indoor premises. Here’s how to calculate BTU for heating in 5 steps:

  1. Measure the length and the width of your rooms. 
  2. Calculate the square feet of each room (by multiplying lengths with widths) and sum them up to get the square footage of your home or office.
  3. Measure the average ceiling height on your premises and multiply that by your square footage.
  4. Сalculate the desired increased temperature — the difference between outdoor and temperature you need indoors.
  5. Multiply the square footage, average ceiling height, desired increased temperature, and sealed building multiplier (equals 0.135).

So the final formula looks like this:

Square footage multiplied x average ceiling height x desired temperature x .135 = BTUs needed per hour.

For a 2000 square foot house with 9 feet ceiling and a 30ºF target temperature, you need:

2000 x 9 x 30 x .135 = 72900 BTUs. 

What’s the conclusion? For a house of your size, you’ll need an HVAC that’s capable of putting at least 72900 BTUs. 

And, as you can see, using a BTU calculator for heat requirements measurement is much easier than doing it by hand.

What Is Your Desired Increased Temperature?

We previously mentioned the desired increased temperature. It’s a crucial measurement needed for the BTU heat load calculator. So, let’s tell you how to calculate it.

  1. First, determine the outside temperature in your location. Use historic average winter temperature in your area because that's when your HVAC will struggle the most.
  2. Take the temperature you’ll want to maintain indoors using your thermostat.
  3. Subtract the outdoor temperature from the desired indoor temperature.

For instance, if you have a 50ºF outside and want 80ºF in your home, the desired increased temperature equals 30ºF.

To Sum Up

Using the formulas above, you should accurately determine the amount of energy to warm (or cool) your room or any mass in it. However, our BTU calculator and specific heat calculator should prove much more comfortable. You can also use our converter to figure out how much kW, Caloris, Joules, Therms, or BTUs you need for your HVAC equipment.

Blackhawk Supply has a wide assortment of HVAC, plumbing, and electrical equipment. Feel free to browse our thermostats, relief valves, heating supplies, and other devices!

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