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Backyard Review

Free tool

How many gallons is my hot tub or pool?

Enter the shape and water depth and get gallons, liters and the weight of the water, so you can dose, heat and place it with real numbers.

ft
ft
ft

Water depth, not wall height.

ft

Same as shallow for a hot tub.

lb

From the maker's spec sheet. Skip it for pools.

gpm

To see how long one full turnover takes.

For a hot tub, use the depth of the water, not the depth of the shell. Seats and footwells mean the real volume is usually a bit less than a straight box, so treat this as an upper estimate.

Water volume

1,283 gal

4,855 liters

Weight of the water

10,699 lb

5.3 tons

Average depth

3.5 ft

49 sq ft surface

Cubic feet

171.5

of water

How this is calculated

Volume = surface area × average depth × 7.48 gallons per cubic foot. Rectangles use length × width, circles use π × radius², and ovals use π ÷ 4 × length × width. Average depth = (shallow + deep) ÷ 2, a good estimate for a straight slope. Water weighs 8.34 lb per gallon, and one gallon is 3.785 liters.

Kidney shapes, benches and steps change the real volume. For an exact figure, use the maker's published capacity, which is the number to use for chemical dosing and the one printed on the manual.

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Quick answers

How do I calculate the gallons in a hot tub or pool?

Multiply the surface area by the average water depth in feet to get cubic feet, then multiply by 7.48 to get gallons. For a rectangle the area is length times width, for a circle it is pi times the radius squared, and for an oval it is pi divided by four times length times width.

How much does a hot tub weigh when it is full?

Water alone weighs 8.34 pounds per gallon, so a 400-gallon tub holds about 3,300 pounds of water on top of the tub's own weight. Bathers add more. Always check the maker's pad requirements.

Why does the gallon number matter?

Chemical doses, heating cost and fill time all scale with volume, so a wrong number means wrong doses. Use the maker's stated capacity when you have it, and this estimate when you do not.

Can I put a hot tub on my deck?

Only if the deck is built or engineered for the filled weight. Many decks are not, and the load is concentrated on the footprint of the tub. Ask a qualified contractor or structural engineer, and follow the manufacturer's instructions.

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