Raised Bed Soil Calculator
Soil volume for a raised garden bed
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Working out soil volume for a raised garden bed is easier with Raised Bed Soil Calculator, which answers as you type. Just enter Length (ft), Width (ft) and Depth (in); Raised Bed Soil updates the result as you type. Every Raised Bed Soil answer can be reproduced by hand. Raised Bed Soil suits budgeting and planning checks. Raised Bed Soil is privacy-first: Home & Garden inputs stay offline. Raised Bed Soil is part of the Home & Garden collection on CalcProMaster, alongside raised bed soil calculator cubic feet quarts bags, free calculators and more. The labels in Raised Bed Soil match the terms in its result. No sign-up or email — Raised Bed Soil answers as you type.
What the defaults give
A 6 × 3 ft bed at 12 inches deep takes 18.0 cubic feet of soil.
That is 12 bags of 1.5 ft³, or 0.67 cubic yards in bulk.
The formula
Volume (ft³) = length × width × depth in inches ÷ 12
Bags = ceil(volume ÷ bag size)
Cubic yards = volume ÷ 27
The division by 12 is the only conversion needed: length and width are already in feet, and depth is the one dimension people measure in inches. Feet times feet times feet gives cubic feet, and 27 cubic feet make a cubic yard.
Worked examples
6 × 3 × 12 in → 18.0 ft³, 12 bags, 0.67 yd³
4 × 2 × 10 in → 6.7 ft³, 5 bags
8 × 4 × 12 in → 32.0 ft³, 22 bags, 1.19 yd³
4 × 4 × 6 in → 8.0 ft³, 6 bags
10 × 4 × 18 in → 60.0 ft³, 40 bags, 2.22 yd³
6 × 3 × 6 in → 9.0 ft³, 6 bags
Fill height, not board height
A bed built from 12-inch boards is not filled to the rim. Leave 2 inches of freeboard so water and mulch stay in, which makes the real depth 10 inches and the real volume 15 ft³ rather than 18. Boards also settle into the ground, and soil compacts by roughly 10% in the first season, so a bed topped up to the line in spring will be low by midsummer.
If the bed sits on compacted subsoil rather than open ground, add a drainage layer of gravel and expect the soil above it to hold less water. If it sits on open ground, roots will reach down and the calculated volume is a starting charge rather than a hard limit.
What goes in the 18 cubic feet
Do not fill a raised bed with topsoil alone. A common blend is roughly 60% topsoil, 30% compost and 10% coarse sand or perlite for drainage; a bed filled with pure compost holds too much water and shrinks dramatically as it decomposes. Bulk delivery is sold by the cubic yard, so 18 ft³ rounds up to one yard with a little spare for settling.
Weight matters for a roof garden or a balcony: soil runs about 75 to 100 lb per cubic foot when damp, which makes 18 ft³ roughly 1,400 to 1,800 lb. Bags are easier to carry but cost noticeably more per cubic foot than a bulk load, which is why the crossover usually sits around half a yard.
Frequently Asked Questions
How much soil for a 6 by 3 foot raised bed?
18 cubic feet at 12 inches deep. That is 12 bags of 1.5 ft³ or 0.67 cubic yards in bulk.
How many bags of soil is 18 cubic feet?
Twelve 1.5 ft³ bags, and the calculator rounds up, so a fractional result still means a whole number of bags to buy.
How do I convert to cubic yards?
Divide cubic feet by 27. At the defaults, 18 ÷ 27 = 0.67 cubic yards, so one bulk yard covers the bed with spare for settling.
Should I fill the bed to the top of the boards?
No. Leave about 2 inches of freeboard so water and mulch stay in, and allow for soil settling roughly 10% in the first season.
What mix should I use?
Roughly 60% topsoil, 30% compost and 10% coarse material for drainage. Pure compost holds too much water and shrinks as it breaks down.
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