Raised Bed Soil Calculator

How this is calculated

A raised bed is a box, so the volume is length x width x depth. Depth is entered in inches and divided by 12 to bring it into feet before multiplying. A cubic yard is 27 cubic feet, by definition. That is the figure used for a bulk delivery. Bag count is the total cubic feet divided by the size of the bag, rounded up. Bag size is an input because it varies far more than people expect: 1, 1.5 and 2 cubic foot bags are all common, and compost is often sold in litres instead. Fill depth is not the same as bed height. Most beds are filled to an inch or two below the rim so watering does not wash soil over the edge, and soil settles in the first season regardless. This assumes a rectangular bed with a flat bottom. For an L-shape or a tiered bed, split it into boxes, run each one, and add the results.

Common questions

How deep does a raised bed need to be?

Six to eight inches suits salad, herbs and most leafy crops. Ten to twelve gives root vegetables and tomatoes somewhere to go. Deeper than that is mostly for comfort — a bed at waist height saves your back, and the extra depth below the root zone is doing nothing but costing you soil.

Bags or bulk?

Compare on volume. A cubic yard is 27 cubic feet, which is 18 bags at 1.5 cubic feet each. Once you are past roughly fifteen or twenty bags, bulk is usually cheaper and always less carrying — but it arrives as a pile on your drive.

Can I fill the bottom with something cheaper?

Partly. Filling the lower third with logs, branches or coarse material reduces the soil you buy and holds moisture as it breaks down. It also sinks noticeably in the first year, so expect to top the bed up.

Why does my bed look lower after a few months?

Because it is. Fresh soil and compost settle and decompose, and most beds drop an inch or two in their first season. That is normal — top it up each spring rather than trying to prevent it.

My bed is not a rectangle. What now?

Split it into boxes, run the calculator for each, and add the cubic feet together. A slight overestimate is the safer error, since the bed will settle anyway.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Raised Bed Soil Calculator at https://www.bfcbrilliance.com/tools/raised-bed-soil-calculator.

What I entered:
- Bed length (ft): ___
- Bed width (ft): ___
- Fill depth (in): ___
- Number of beds (beds): ___
- Bag size (cu ft): ___

What it calculated:
- Cubic feet of soil: ___
- Cubic yards: ___
- Bags to buy: ___
- Growing area: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

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