Sizing equipment is one of the few places where bigger is not better. An oversized air conditioner short-cycles and leaves the room clammy, and an undersized heater runs forever. These calculators size equipment from room dimensions and conditions, work out the generator or tankless water heater that suits your loads, and convert pool and rainwater volumes into gallons.
Heating, Cooling, Water & Power calculators
- AC Size Calculator (BTU)What BTU air conditioner you need for a room.
- Space Heater Size CalculatorWatts of heater for a room, plus running cost.
- Pool Volume CalculatorGallons in a rectangular, round or oval pool.
- Rainwater Collection CalculatorGallons you can collect from a roof, and how many rain barrels.
- Generator Size CalculatorWhat wattage generator you need to run your appliances.
- Tankless Water Heater CalculatorGPM, BTU and kW needed for a tankless water heater.
- Ceiling Fan Size CalculatorBlade span and downrod length for a room.
- Water Softener Size CalculatorGrain capacity of softener for your household and water hardness.
- Portable Power Station Size CalculatorBattery capacity (Wh) and output (W) to run your devices, plus solar panels.
- Battery & Power Station Runtime CalculatorHow many hours a battery or power station will run a device.
- Furnace Size CalculatorBTU output and input rating of a furnace for your house.
Guides
- How to Calculate Pool Volume in Gallons (Any Shape)Formulas for the volume of rectangular, round and oval pools in gallons, with a chart of common sizes, and why you need the number for chemicals and filling.
- Tankless Water Heater Sizing: GPM, BTU and kW ExplainedHow to size a tankless water heater from flow rate and temperature rise, with a BTU chart by GPM, gas versus electric, and why electric units need so many amps.
- What Size Air Conditioner Do I Need? BTU Chart by Room SizeChoose the right air conditioner size: BTU needed by room size, how to adjust for sun, ceilings and people, and why bigger is not better.
- What Size Generator Do I Need? Wattage Chart for Your HomeHow to size a portable or standby generator: running vs starting watts, a wattage chart for common appliances, and real examples from 2,000 to 20,000 watts.
- What Size Portable Power Station Do I Need? Wh, Watts & SolarHow to size a portable power station: watt-hours vs watts, how long it runs common devices, a wattage and running-cost chart, and how many solar panels recharge it.
- What Size Water Softener Do I Need? Grain Capacity ChartHow to size a water softener from household size and water hardness, with a grain capacity chart, hardness levels, the iron adjustment and regeneration.