SettingsSettings for this calculationUS
The circular area you need to cover, in square feet.
This is the finished area of the circle itself. If you are ordering material, add the waste allowance afterwards rather than inflating the area here, or the radius you set out will be wrong.
Required radius
9.772 ft
Radius = √(area ÷ π), the exact inverse of A = πr². Set out from the centre with a string line at this radius; doubling it gives the diameter you need to fit the space.
They open the calculator with your figures already in it
Area to Radius Calculator: 9.77 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Area of a circle A = pi x r^2, so r = sqrt(A / pi)
Inputs used
- Target area (sq ft)
- 300
Confidence note: Radius = √(area ÷ π), the exact inverse of A = πr². Set out from the centre with a string line at this radius; doubling it gives the diameter you need to fit the space.
What this calculation does not cover
- The page returns a radius and stops there. Everything restraining the edge — kerb, edging strip, formwork for a ring beam, the haunch of concrete behind it — is bought by the running foot off the circumference, which is 2πr and is not shown: a 300 sq ft circle is just under 9 ft 10 in of radius and a little over 61 ft of perimeter. Order edging against the radius, or against the diameter, and the job comes up short.
- Cut waste on a circle is not the allowance you would use on a rectangle, because cut edge per square foot is 2/r and climbs as the circle shrinks. A circle of 10 ft radius carries twice the cut perimeter per square foot of one at 20 ft, and almost nothing trimmed off a curve is reusable — so the smaller the feature, the larger the percentage that has to go on top of the order.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Area of a circle A = pi x r^2, so r = sqrt(A / pi)
Cite this page
Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.
Circular setting-out usually starts from the wrong end: you know how much space a patio, tank base or planting bed has to provide, and you need the radius that delivers it. The square root of area over pi answers that exactly. Two things trip people up on site. The radius is measured from the centre, so the space actually consumed is twice this figure plus any edging — check that against the width available before pegging out. And the area entered should be the finished circle, not the material order: adding a cutting allowance to the area before converting inflates the radius and produces a physically larger circle than intended, rather than a correctly sized one with spare material. Apply waste to the quantity, never to the geometry.