Raised Bed Soil Calculator: Full Fill, Top-Ups & Bags
Use inside bed dimensions and the depth you actually want to add to estimate soil volume and whole bags.
Worked project: top up 3 inches, not the full 12-inch bed
- Measure the inside of one bed: 8 ft long × 4 ft wide. For a 3-inch top-up, enter Fill depth = 3 in, Identical beds = 1, Extra fill allowance = 0%, and Bag volume = 2 ft³.
- Convert the added depth: 3 ÷ 12 = 0.25 ft. Volume = 8 × 4 × 0.25 = 8 ft³ before any allowance. At 2 ft³ per bag, that is 4 whole bags.
- For comparison, filling the same inside footprint to a full 12-inch depth means 12 ÷ 12 = 1 ft, so 8 × 4 × 1 = 32 ft³, or 16 bags of 2 ft³, before any allowance. Do not enter the full frame height when you only need the missing 3 inches.
Keep the scope clear: Use inside measurements and the actual additional fill depth, not outside lumber dimensions. The calculator does not sense existing soil or subtract it automatically: you enter the depth to add. These examples use zero extra allowance; any chosen allowance increases the volume before whole bags are rounded up. Volume arithmetic does not prescribe a soil blend, forecast settlement, or design drainage or bed structure.
To reproduce this project, enter the values in the steps above. Reset to example values restores the calculator’s separate default example.
How this works
Inside length × width × depth × number of identical beds, plus chosen allowance.
Example
Using the example inputs, total fill volume is 32 ft³.
- Inside length
- 8 ft
- Inside width
- 4 ft
- Fill depth
- 12 in
- Identical beds
- 1
- Extra fill allowance
- 0 %
- Bag volume
- 2 cu ft
- Total fill volume
- 32 ft³
Use inside measurements and desired fill depth, not outside lumber dimensions.
Scope and assumptions
Volume only; does not prescribe soil blends, fertilizer, drainage or bed structure.
Related quantity-calculation reference