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Pool Size Calculator

The pool size calculator turns two or three measurements into every number a builder or supplier will ask for. You get surface area, perimeter, water volume and a deck estimate on one screen. It suits people planning a build as much as owners ordering a cover or a liner.

Pool size calculator illustration comparing rectangle, oval and kidney pool shapes with a tape measure

Run the numbers

Formula used

Area = Length x Width. Perimeter = 2 x (Length + Width). Volume = Area x Depth x 7.48

Your result

Surface area
800 sq ft
Perimeter
120.0 ft
Water volume
29,922 gallons
Deck area
544 sq ft

Results update as you type. Round up when you buy materials.

How the pool size calculator works

Surface area drives liner and cover pricing. Perimeter drives coping, fencing and edge tile counts. Volume drives chemicals and equipment sizing. This tool prints all three from the same inputs.

The deck estimate assumes a walkway of the width you pick running all the way around the pool, which is the layout most contractors quote first.

The formula, step by step

Area = Length x Width. Perimeter = 2 x (Length + Width). Volume = Area x Depth x 7.48

  • Area for a rectangle is length times width.
  • Perimeter for a rectangle is two times the sum of length and width.
  • Round pools use 3.14 x diameter for perimeter and 3.14 x radius squared for area.
  • Deck area = area of the pool plus deck, minus the pool area itself.

Worked example

A 20 by 40 foot rectangle pool with an average depth of 5 feet.

Area = 800 square feet. Perimeter = 2 x (20 + 40) = 120 feet.

Volume = 800 x 5 x 7.48 = 29,920 gallons. A 4 foot deck around it adds 544 square feet of concrete.

Watch it done

This short video walks through the same job in real life, so you can match what you see on screen to what you do at the pool.

Video guide: How to Measure and Size a Pool by Leslie's. Video hosted on YouTube.

Tips before you start

Standard residential rectangles run 12 by 24, 16 by 32 and 20 by 40 feet. Lap swimmers usually want at least 40 feet of straight length.

Check your setback rules before you settle on a size. Many towns require the water edge to sit 5 to 10 feet from a property line, and the deck counts toward lot coverage.

Pool Size Calculator FAQs

What is a good pool size for a family?

A 16 by 32 foot pool with depth from 3 to 6 feet fits most families of four. It gives room to swim and stays cheaper to heat than a 20 by 40.

How much deck space should I plan?

Four feet all the way around is the working minimum. Six to eight feet on one side gives room for chairs and a table.

Does pool size change my running cost?

Yes. A bigger surface area loses more heat and water to evaporation, and a bigger volume needs more chemicals every week.

What size pool needs a permit?

Most areas require a permit for any pool deeper than 24 inches, no matter the footprint. Check with your local building office before you dig.