# Pool Size Calculator

Calculate pool size in gallons for any shape. Pool calculator for rectangular, round, oval, and kidney pools with surface area and pump GPM sizing.

## What this calculates

Find out exactly how many gallons your pool holds. This pool size calculator handles rectangular, round, oval, and kidney-shaped pools, plus sloped bottoms with a shallow and deep end. You get volume in gallons and liters, total surface area, and the minimum pump flow rate for a full 6-hour turnover. Knowing your pool size is step one for chemical dosing, pump sizing, and heater selection.

## Inputs

- **Pool Shape** — options: Rectangular, Round / Circular, Oval, Kidney / Freeform — Above ground pool volume calculator covers round and oval liner pools
- **Length (or Diameter)** (ft) — min 1, max 300 — Longest side. For round pools, enter the diameter.
- **Width** (ft) — min 0, max 200 — Ignored for round pools
- **Depth Input** — options: Single average depth, Shallow end + deep end — Choose sloped for pools with a deep end
- **Average Depth** (ft) — min 0, max 30 — Used when depth input = single average depth
- **Shallow End Depth** (ft) — min 0, max 15 — Used when depth input = shallow + deep
- **Deep End Depth** (ft) — min 0, max 30 — Used when depth input = shallow + deep

## Outputs

- **Pool Volume** — Total water capacity in US gallons
- **Pool Volume (metric)**
- **Surface Area**
- **Recommended Pump Flow (6-hr turnover)** — Minimum GPM for a full 6-hour turnover
- **Average Depth Used**

## Details

Pool Volume Formulas

  - Rectangular: Length x Width x Avg Depth x 7.48 gal/ft^3

  - Round pool volume calculator: pi x Radius^2 x Avg Depth x 7.48

  - Oval: pi x (Length/2) x (Width/2) x Avg Depth x 7.48

  - Kidney / freeform: Length x Width x Avg Depth x 7.0 (irregular bottom coefficient)

For sloped pools with a shallow and deep end, average depth equals (shallow + deep) / 2. This works for most residential pools where the floor slopes evenly.

Typical Pool Sizes

  - Small round above-ground (12 ft x 48 in): about 3,400 gallons

  - Medium round above-ground (18 ft x 52 in): about 8,600 gallons

  - Small rectangular (16 x 32 ft, avg 5 ft): about 19,200 gallons

  - Standard in-ground (20 x 40 ft, 3-8 ft slope): about 33,000 gallons

  - Large in-ground (25 x 50 ft, 4-10 ft slope): about 65,400 gallons

Why Pool Size Matters

Gallons drive almost every other pool decision. Every chemical dose, from chlorine to cyanuric acid, scales directly with pool volume. Filter capacity, pump horsepower, heater BTU, and salt system size all depend on gallons. A small pool gallon calculator gives you a fast check before shopping for equipment or chemicals. Even a 10% error in volume means the same 10% error in chlorine, which matters for sanitation.

Above Ground vs In-Ground

An above ground pool volume calculator uses the same math as an in-ground calculator. Pick round for most Intex or soft-sided pools, oval for long above-grounds, rectangular for liner pools, and kidney for freeform gunite shapes. Above-ground pools usually have a consistent depth, so the single-average-depth option works fine. In-ground pools almost always have a sloped bottom, so use the shallow + deep option.

## Frequently Asked Questions

**Q: How do I figure out how many gallons my pool holds?**

A: Multiply the surface area by the average depth, then by 7.48 (gallons per cubic foot). A 16 x 32 ft rectangular pool with 5 ft average depth is 16 x 32 x 5 x 7.48 = about 19,150 gallons. For round pools, use pi x radius squared. For sloped pools, average the shallow and deep ends.

**Q: Does this work as an above ground pool volume calculator?**

A: Yes. Round and oval Intex, Bestway, and Coleman pools use the same formulas. A 24-ft round x 52-in above-ground pool is pi x 12^2 x 4.33 x 7.48 = about 14,650 gallons. Most above-ground pools have a single flat bottom, so use the single-average-depth option.

**Q: What is a 6-hour turnover and why does the calculator show it?**

A: Turnover is how long your pump takes to circulate the entire pool volume through the filter once. The commercial and best-practice standard is 6 hours. The calculator divides gallons by 360 minutes (6 x 60) to give the minimum GPM your pump needs. A 20,000 gallon pool needs about 55 GPM for a 6-hour turnover.

**Q: How accurate is this small pool gallon calculator for freeform shapes?**

A: For true freeform pools (kidney, lagoon, lazy-L), the 7.0 coefficient is an industry-standard approximation that typically lands within 5-10% of actual volume. For more precision, measure the pool in sections (rectangular main body + circular spa) and add the volumes. A dye-and-timer test also works if you know your pump GPM.

**Q: Should I use inside or outside measurements for my pool?**

A: Always use inside water measurements. For a vinyl liner pool, measure between the liner walls at the water line. For a concrete pool, measure waterline to waterline across the interior. Don't include the coping or deck; that padding will overstate volume by 10-20%.

**Q: How much water do I lose to evaporation?**

A: A typical backyard pool loses about 1/4 inch per day to evaporation in summer, which is roughly 150-200 gallons per day for a 500 sq ft surface. Wind, temperature, and humidity change that. If you lose more than 1/2 inch per day without heavy use, check for a leak.

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Source: https://vastcalc.com/calculators/everyday/pool
Category: Everyday Life
Last updated: 2026-04-08