b2KIT

Raised Bed Soil Calculator

Calculate cubic feet of soil mix needed to fill raised garden beds of any shape.

Tested tool guide Tested browser tools Checked August 16, 2026

What Raised Bed Soil Calculator does, with a checked example

Raised beds hold more than they look like they should: a 4-by-8-foot bed barely knee-high swallows more than a cubic yard of soil. This tool turns bed dimensions into the cubic feet of soil mix needed to fill them, including footprints beyond plain rectangles. You enter length, width, and depth; it multiplies area by depth, converting inches to feet so the answer lands in cubic feet, the unit printed on soil bags. The figure people most often get wrong is depth: enter how deep you will actually fill the bed, not the height of the boards, and measure inside the frame.

Worked example

A concrete input and expected output from the current implementation.

Input

Length 6 ft, width 3 ft, depth 10 in

Expected output

15 cubic feet of soil mix

The footprint is 6 x 3 = 18 square feet, and 10 inches converts to 10/12 of a foot, so the volume is 18 x 10/12 = 15 cubic feet. Depth entered in inches is divided by 12 before the final multiplication.

How the result is produced

1

Footprint times depth

Volume is footprint area multiplied by depth, all in feet. For a rectangular bed the tool multiplies length by width by depth, first dividing any inch measurement by 12: 10 inches becomes 0.833 foot. Because soil is sold by volume, not weight, the answer in cubic feet converts directly to bag counts and delivery quantities.

2

Any footprint, one rule

A non-rectangular bed follows the same rule: find the area of its footprint, then multiply by depth. A circular bed uses pi times the radius squared; an L-shaped bed is two rectangles added together. The result stays in cubic feet. Bulk soil is quoted per cubic yard, so divide the figure by 27 to convert.

Good uses

  • Planning the first fill of a new bed before a shopping trip, so you buy the right number of bags in one visit.
  • Comparing bed depths: a 6-inch fill versus a 12-inch fill over the same footprint shows exactly how much more soil the deeper bed costs.
  • Checking a bulk order: converting the cubic feet figure to cubic yards (divide by 27) before calling the landscape supplier.

Limits and checks

  • Measure inside the frame: exterior dimensions overcount, especially with thick wood corners, and depth should be the fill height, not the height of the boards.
  • The result is geometric volume, not what you will actually buy. Fresh mix settles 10-20 percent after watering and as compost breaks down, so the real order is usually larger; add a buffer yourself.
  • The raw number is not a bag count. Bag sizes run from about 1 to 3 cubic feet depending on the product, and bulk deliveries quote cubic yards (27 cubic feet), so divide by the exact unit you are buying.

Common questions

My bed is 4 by 8 feet and 12 inches deep. How many bags of soil do I need?

That bed takes 32 cubic feet (4 x 8 x 1). In 2-cubic-foot bags that is 16 bags; in 1.5-cubic-foot bags it is about 22 (21.33, rounded up). The tool returns cubic feet, so you divide by the bag size you actually buy, and because soil settles, one or two extra bags are rarely wasted.

Why does my last delivery look like so much more soil than the calculator says my bed holds?

Delivered soil is measured loose and fluffy, while the calculator gives the bed volume at its settled, in-place density. The same load packs down noticeably once watered and tamped, which is why orders sized exactly to the calculator often run short. Ordering 10-15 percent extra is the usual fix.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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