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Radius to Area Calculator

Convert a measured radius into circular area for material take-off on curved and round work.

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

Circular area

314.16 sq ft

High confidence

Area = π × r², computed exactly. Curved work generates more offcut than rectangular work — allow a wider waste margin than you would on a straight run.

Going the other way — from a measured radius to an area — is the take-off step for anything round: a circular slab, a tank base, a bandstand deck, a turfed island. The arithmetic is trivial, and the error that costs money is confusing radius with diameter. Because area goes with the square of the radius, entering a diameter by mistake reports four times the true area, which on a concrete pour is an expensive lorry to send away. Measure from the centre, or measure across and halve it. Worth noting too that circular work wastes more material than rectangular work of the same area: sheet goods, pavers and tiles all have to be cut to a curve, and offcuts from the perimeter are rarely reusable, so a waste allowance appropriate to a straight run will leave you short.

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

Your workspace

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Frequently asked questions

I measured across the circle. Can I use that?
Not directly — that is the diameter. Halve it first. Because area scales with the square of the radius, entering a diameter reports four times the true area, which on a concrete order is an expensive mistake.
How much extra material should I allow for a circle?
More than for a rectangle of the same area. Every perimeter piece is cut to a curve and the offcuts are rarely reusable, so allowances that work on straight runs tend to leave you short on round work.
What about a ring or an annulus?
Calculate the outer circle and the inner circle separately and subtract. This calculator handles a full disc; a path around a circular bed is the difference between two of them.