By Azura · Updated June 2026 · Raised Garden Hub is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no extra cost to you.
Getting the size right is the difference between a bed you love and one you fight with all season. There are only three numbers that matter: depth, width, and length — and two of them have clear right answers.
Start here: get a recommendation
Raised Bed Size Advisor
Tell us what you'll grow and we'll suggest the right dimensions.
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See recommended beds on Amazon →Depth: match it to your roots
Depth is the number most beginners get wrong. Too shallow and roots hit the bottom; too deep and you overpay for soil.
- 6–8 inches — lettuce, spinach, herbs, radishes
- 12 inches — the all-rounder; suits most vegetables
- 18 inches+ — carrots, potatoes, parsnips, and big tomato plants
Width: never more than 4 feet
You should be able to reach the middle of the bed without stepping in it (stepping in compacts the soil). The rule:
- Reaching from both sides: 4 feet max
- Against a wall or fence (one side): 2–3 feet max
Length: whatever fits your space
Length is flexible. The most popular size is 4×8 ft because lumber and bed kits come in those dimensions. Longer than 8 ft and the bed can bow, so add a cross-support.
How much soil will that need?
Deep beds drink soil. Punch your dimensions in below to see the exact volume and how many bags to buy — plus a Mel’s Mix recipe.
Raised Bed Soil Calculator
Enter your bed size to see exactly how much soil you need.
Mel's Mix recipe (equal thirds)
- — cu ft compost / manure
- — cu ft peat moss or coco coir
- — cu ft coarse vermiculite
Tip: Filling a deep bed? Tick the hugelkultur box in the calculator above — filling the bottom third with logs and branches cuts your soil bill by about a third. See our full guide to filling a raised bed cheaply.
Next steps
Once you know your size, pick the bed itself in our best raised garden beds of 2026 roundup, or settle the big material question: metal vs wood.