Raised Garden Bed Calculator
Boards, posts, screws and soil — with the height your bed will actually be.
Your bed
Materials list
Generated by AllUnits.io — allunits.io/calculators/raised-bed
How this calculator figures it
Frame height is counted in whole boards at their actual dressed width — a 2×6 is 5½ inches and a 2×12 is 11¼ inches under the American Softwood Lumber Standard (NIST PS 20) — so a "12-inch" bed is really 11 inches in two courses of 2×6, and this tool says so. Soil is length × width × the finished height, plus 15–20% for settling; bagged figures use the standard 0.75 cu ft per 40 lb bag of topsoil.
How it works
Worked example — a 4 × 8 ft bed asking for 12 inches, built from 2×6: two courses of 5½" give a finished height of 11 inches, so the frame takes 4 side boards, 4 end boards, 4 corner posts and 32 screws, and the box holds 29.3 cu ft of soil. Filled to a true 12 inches that same bed would take 32 cu ft — 1.19 cubic yards — and you would order about 1.4 cubic yards to allow for settling.
Raised bed FAQs
How deep should a raised garden bed be?
At least 12 inches of soil for most vegetables, and 12–18 inches is better — deeper beds hold moisture longer and give roots more room. Per University of Minnesota Extension guidance.
Why is my 12-inch bed only 11 inches?
Lumber is sold by nominal size but milled smaller: a 2×6 is 5½ inches wide, so two courses make 11 inches, not 12. A single 2×12 is 11¼ inches. Actual dressed sizes come from NIST PS 20 — most raised-bed calculators quietly use the nominal number.
How much soil does a 4×8 bed need?
Filled 12 inches deep it holds 32 cubic feet, about 1.19 cubic yards. Order 15–20% extra for settling — roughly 1.4 cubic yards.
What wood is safe for a vegetable bed?
Untreated cedar is the standard choice: naturally decay-resistant, with no preservatives next to food crops. Redwood behaves similarly. Douglas fir and pine cost less but rot faster.
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Related calculators & sources
Filling more than one bed? The Topsoil Calculator works in bulk yards and bags, and the Mulch Calculator covers the paths between beds. Pricing the lumber: Board Foot Calculator. Dressed sizes come from NIST PS 20; depth, settling and material guidance from raised-bed sources. Convert measurements with the volume and length converters.
Estimates for planning and purchasing. Not engineering or code-compliance advice — confirm structural work with your local building department.