Home and Outdoor Equipment Calculators
HomeGearCalc is a set of free browser calculators for home equipment and aquariums. Size a propane tank's burn time, pool salt, a portable generator, a room air conditioner, or a tankless water heater. The aquarium section covers gallons, standard tank dimensions, heater watts, and a stocking rule of thumb.
Every calculator runs on this page's device. Nothing you type is sent to a server. Results are estimates for planning, not a substitute for the rating plate or a licensed installer.
Home equipment
Propane tank calculator
Hours of burn from tank gallons, fill level, and the appliance BTU per hour. Uses 91,502 BTU per gallon.
Pool salt calculator
Pounds of salt to move a pool from the current ppm to a target, counted in 40 lb bags.
Generator size calculator
Running watts, the largest motor surge, and 20 percent headroom.
Air conditioner BTU calculator
Room area against the ENERGY STAR size table, then sun, people, and kitchen.
Tankless water heater calculator
Peak flow and temperature rise, in electric kilowatts and gas BTU per hour.
Aquarium
Aquarium volume calculator
How many gallons a rectangle, cylinder, bow-front, hexagon, or corner tank holds.
Fish tank dimensions
10 gallon length and the outside size of common 20, 29, 55, and 75 gallon tanks.
Aquarium heater size
Watts from gallons and how far the water must stay above the room.
Aquarium stocking calculator
The inch-per-gallon rule of thumb, with stricter settings for heavier fish.
How to use a result
Start with the number on the appliance, the test kit, or the tape measure. The calculators apply one published formula and show the steps on that tool's page. If a tank, pool, or room does not match the preset, type the measurement you actually have. A generator watt total is only as good as the nameplate watts you add. A fish-tank gallon total is the water you measured, not the number printed on the carton.
Frequently asked questions
What size generator do I need to run a house?
Essentials such as a fridge, sump pump, lights, and a router often land around 3,000 to 5,000 running watts once the largest motor surge and 20 percent headroom are included. Central air or an electric water heater can push that much higher. Use the generator calculator with your own nameplate watts.
How long does a 20 lb propane tank last?
A 20 lb grill tank holds about 4.7 gallons. At 91,502 BTU per gallon, a 36,000 BTU per hour burner on full lasts about 11.9 hours. At half the burner setting it lasts about twice as long.
How many gallons is my fish tank?
Measure the water in inches and divide length times width times height by 231. A water box of 20 by 10 by 12 inches is 10.39 US gallons. The aquarium volume calculator also covers cylinders, bow-fronts, hexagons, and corner tanks.
Are these results exact?
No. They are planning estimates from published rules and the constants named on each page. Check the rating plate, the pool test kit, or a thermometer before you buy or install anything.