Free pool volume calculator

Pool gallons with the sloping floor counted properly

Choose a rectangular, round, oval or kidney outline, measure the water at the surface, and describe the floor — one depth, one slope, or the usual shallow flat, slope and deep-end hopper — and this returns the capacity in US gallons, liters and cubic feet. The floor is where it differs from every other pool page: averaging the shallow and deep depths assumes the pool spends as much of its length deep as shallow, and on a 32 by 16 ft pool with an 8 ft hopper that shortcut invents 1,077 gallons. Both figures are shown, so the gap is visible instead of asserted.

100% free
No signup
4 outlines
Weighted floor average
Gallons per inch

Pool shape

Straight walls and square corners, in-ground or a framed above-ground box.

Length at the water (feet)Width, or across the first lobe (feet)

Floor

Shallow end (feet)Deep end (feet)

Both taken vertically from the water surface, not down the face of the slope — a tape laid on the ramp reads the hypotenuse and puts every figure here high.

Shallow flat runs (feet)Deep flat runs (feet)

Drop the water line by (inches)For a partial drain: closing down, or diluting a reading that has climbed too high to fix with anything you add.

This pool holds

20,945 US gal

Liters: 79,287
Cubic feet: 2,800
Water surface: 512 sq ft
Average depth: 5.47 ft
Every inch of depth: 319 gal

Where the average depth came from

12 ft at 3.5 ft
12 ft averaging 5.75 ft on the slope
8 ft at 8 ft
weighted over 32 ft = 5.47 ft

Halving the shallow and deep ends on their own would call it 5.75 ft and 22,023 gal — 1,077 gal more than the floor really holds, or 5.14%.

Dropping it 4 in

Takes out 1,277 gal and leaves 19,669 gal behind. Surface area is the same at every level in a straight-walled pool, so the water line falls at a steady 319 gallons an inch until it reaches the slope.

How to calculate pool volume

Three steps, and only the second one is where pool calculators disagree with each other.

Pick the outline and measure the water, not the deck
Rectangular and round take one or two numbers; an oval takes its length and width; a kidney takes the length plus the width across each lobe separately, because the trade formula works on the sum of the two. Measure to the inside of the wall at the water line, not to the outside of the coping or the top rail of an above-ground.
Describe the floor honestly
One depth throughout is an above-ground pool sitting on leveled sand. A single slope is a wall-to-wall ramp, which is rarer than people think. Most in-ground pools are the third option: a flat shallow end, a slope, and a flat deep-end hopper — so type how many feet each of the two flats runs, and the slope is whatever is left over.
Read the gallons and carry them to the chemistry
The headline figure is US gallons, with liters, cubic feet, the water surface and the weighted average depth beside it. Two extra numbers earn their place: gallons per inch of depth, which is what topping up and evaporation are measured in, and what a partial drain of any depth actually removes.

Technical specifications

Outlines	Rectangular, round, oval and kidney
Floor profiles	One depth, a single wall-to-wall slope, or shallow flat plus slope plus deep flat
Average depth	Weighted by the length of each run, not (shallow + deep) ÷ 2
Oval factor	0.7854 of its bounding rectangle — exact for an ellipse, not an approximation
Kidney factor	0.45 × (width A + width B) × length, the pool trade's fit for a two-lobed outline
Worked example	32 × 16 ft, 3' 6" to 8' with a 12 ft shallow flat and an 8 ft hopper: 20,945 gal, where the two-number shortcut reports 22,023 — a 1,077 gal gap, printed on screen rather than asserted
Water per inch	0.62 gal per square foot of surface, so 319 gal an inch on a 32 × 16
Stored or sent	Nothing — no dimensions, no readings, no account

Frequently asked questions

How many gallons is a 32 by 16 foot pool?

Anywhere from 15,320 to 22,023, and the floor decides which. A flat 4 ft depth gives 15,320 gallons. The same rectangle with a 3 ft 6 in shallow end, an 8 ft deep end, a 12 ft shallow flat and an 8 ft hopper holds 20,945. Averaging just the shallow and deep figures — the shortcut almost every pool page takes — reports 22,023, which is 1,077 gallons of water that is not in the pool.

Where exactly do I measure the depth from?

Straight down from the surface of the water. Measuring from the coping, the deck or the top rail adds the freeboard to every single gallon, and freeboard is not water. This catches out above-ground owners hardest, because the wall height is printed on the box and the water depth is not: a 52 in wall is filled to the middle of the skimmer mouth, four to six inches down, so it stands in about 46 in.

How many gallons is a 24 foot round above-ground pool?

About 13,536 with 48 in of water in it. The floor of a round above-ground pool is laid flat on sand, so there is no averaging to do: the surface is 452 sq ft, four feet deep is 1,810 cubic feet, and that is 13,536 gallons. Fill the same pool an inch lower and you lose 282 gallons, which is why the depth reading matters more than the diameter on the label.

Why does averaging the shallow and deep ends overstate a pool?

Because the deep end is almost always the shortest section of the floor. A midpoint average silently assumes the pool spends as much length deep as it does shallow, and a typical hopper is eight or ten feet of a thirty-two foot pool with the shallow flat running twelve or more. The weighted figure on this page multiplies each run by its own depth, which is the same arithmetic a surveyor would do and about 5% lower on the pool it opens with.

How much water is one inch of depth?

0.62 gallons for every square foot of water surface. That single conversion is worth memorizing: a 32 by 16 ft pool has 512 sq ft of surface, so every inch is 319 gallons, up or down, whatever the floor is doing underneath. It is the number behind a top-up, an evaporation estimate and the bucket test that separates a leak from a hot week.

My salt or stabilizer reading is too high. How much do I drain?

The fraction you drain is the fraction you remove, because nothing you add takes either of them out. Salt and cyanuric acid leave a pool only with the water, so cutting a reading by a quarter means replacing a quarter of the volume — and the gallons per inch figure on this page turns that into a depth you can watch on the tile line. The pool salt calculator does the arithmetic in the other direction, from a reading to bags.

About the sloping floor, and the gallons every dose depends on

A pool is a manufactured object, so its outline is the easy half. A rectangle is its own area, a circle and an ellipse are 0.7854 of the box they sit in, and the kidney has a trade rule — 0.45 times the sum of the two lobe widths times the length — which is a fit rather than a derivation and is good to a few percent. None of that is where pool volumes go wrong. The floor is. Almost every calculator on the web asks for a shallow depth and a deep depth, adds them and halves them, which is only correct if the floor is one unbroken ramp from wall to wall. Real in-ground pools are not built that way: they are a long flat shallow end, a transition slope, and a short flat hopper at the deep end, and the correct average weights each of those three by the distance it runs. On a 32 by 16 ft pool the shortcut is 5.1% high, which sounds small until you notice it is the same 5.1% on every calculation you make from it for as long as you own the pool.

That is the real reason this number matters. Capacity is not a fact anyone wants for its own sake — it is the denominator under every chemical decision, and pool chemistry is written per 10,000 gallons. A volume that runs 5% high makes every dose 5% strong, forever, and the reading that comes back is then corrected with another dose calculated from the same wrong number. Take the gallons figure from here to the pool salt calculator and to the chlorine, acid and stabilizer adjustments, and it is worth spending ten minutes with a tape on the shallow flat rather than guessing at it, because that ten minutes is amortized over years.

Two figures on this page have nothing to do with chemistry. Gallons per inch is constant in a straight-walled pool — 0.62 gallons for each square foot of surface — so a water line that drops faster than a quarter of an inch on a still summer day is worth investigating, and the bucket test, which floats a bucket at the same level and compares the two, settles evaporation against a leak without needing any number at all. The partial-drain figure is the other one: salt and cyanuric acid can only be taken out with the water, so the depth you have to pull is a real, plannable quantity. And when the water is finished, the ring around it is a different trade entirely — deck slab quantities and the price of them are on the concrete cost calculator, and the surround area itself is quickest to work out on the square footage calculator.

Your pool dimensions are not collected

Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.

Nothing about the pool — its size, its shape, the readings that made you look up a drain volume — is transmitted or retained. There is no saved profile to come back to, which is the trade-off for a page that asks nothing of you before it answers.