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Area to Radius Calculator

Work out the radius of a circle that encloses a given area — for patios, tanks, planting beds and turning circles.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Required radius

9.77 ft

High confidence

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.

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.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Area of a circle A = pi x r^2, so r = sqrt(A / pi)

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.

Frequently asked questions

Should I add waste before or after converting?
After. Adding a cutting allowance to the area first inflates the radius and gives you a physically bigger circle rather than a correctly sized one with spare material. Convert the finished area, set out to that radius, then add waste to the quantity you order.
How much space does the finished circle actually need?
Twice this radius, plus any edging, kerb or working room. It is worth checking that against the width available before pegging out — a circle that fits on paper often does not once a restraint edge is added.
Does this work in metric?
The maths is unit-agnostic, but this calculator is set up in feet and square feet. Enter square metres and you will get metres out, since the square root of area over pi carries the units through unchanged.