Raised Garden Bed Soil Calculator
"How much soil for a 4×8 raised bed?" is one of gardening's most-Googled questions, and the honest answer is: it depends entirely on the height. This calculator turns your bed's exact dimensions into cubic feet and bags, and splits the total into the classic 60/30/10 mix of topsoil, compost, and aeration material.
How this calculator works
Volume per bed = length × width × height; the calculator multiplies by your bed count and presents the total three ways: cubic feet, 1.5 cu ft bags (the common garden-soil bag), and cubic yards for bulk orders. The suggested mix is 60% topsoil, 30% compost, and 10% aeration material (perlite, coarse sand, or pine fines).
Frequently asked questions
How much soil do I need for a 4x8 raised bed?
At 12" tall: 32 cubic feet, which is about 21 bags of 1.5 cu ft or 1.2 cubic yards in bulk. At 6" tall it's half that (16 cu ft ≈ 11 bags). Bulk 'raised bed mix' by the yard is usually 40–60% cheaper than bagged once you need more than one bed.
What is the best soil mix for raised beds?
A proven recipe is 60% quality topsoil, 30% compost, 10% aeration (perlite, pumice, or pine fines). Pure compost is too rich and slumps; pure topsoil compacts. Mel's Mix (1/3 peat, 1/3 vermiculite, 1/3 compost) works too but costs roughly triple.
Do I need to replace raised bed soil every year?
No — just top it up. Beds settle 1–2" per season as organic matter breaks down; refresh with an inch or two of compost each spring. A full soil replacement is only warranted after disease problems like verticillium wilt.