From measured space to purchasable material
Raised-bed volume should be measured inside the walls and below the intended finished soil line. This calculator subtracts an unfilled headspace and an optional lower filler layer, then divides the remaining volume into three user-selected blend components. It reports each component in cubic feet and whole bags. The percentages describe your chosen recipe; they are not a universal growing recommendation. Bed materials, plant needs, drainage and the suitability of a lower filler layer should be considered before relying on the quantity list.
Measure, select yield and round the order
- Measure the interior rather than outside lumber dimensions.
- Subtract top headspace and any intentionally excluded lower layer.
- Enter a suitable blend recipe and round each component separately.
Net requirement and purchase calculation
A worked example
Two 8 × 4 ft beds, 18 in high with 2 in headspace, need 85.33 ft³ of mix. A 50/30/20 split gives 42.67, 25.60 and 17.07 ft³ respectively.
Raised Bed Soil: what changes the result?
Compare the layer or product assumptions behind the material order. The comparisons below are calculated from this page’s default example. Each row changes only the named input; all other inputs stay at their displayed example values. These are mathematical scenarios, not measurements from a completed project.
| Changed assumption | Default input | Comparison input | Result: default → comparison |
|---|---|---|---|
| Inside bed length | 8 ft | 9.6 ft | Growing-mix volume: 85.3333 → 102.4 cu ft Soil component: 42.6667 → 51.2 cu ft |
| Inside bed width | 4 ft | 4.8 ft | Growing-mix volume: 85.3333 → 102.4 cu ft Soil component: 42.6667 → 51.2 cu ft |
| Inside bed height | 18 in | 21.6 in | Growing-mix volume: 85.3333 → 104.5333 cu ft Soil component: 42.6667 → 52.2667 cu ft |
| Unfilled space at top | 2 in | 2.4 in | Growing-mix volume: 85.3333 → 83.2 cu ft Soil component: 42.6667 → 41.6 cu ft |
Displayed values are rounded. Whole-pack results change in steps; continuous quantities may change before a new pack is needed. To compare your actual project, enter your dimensions above, save a scenario, then change one assumption.
Coverage, allowance and purchasing limits
- The third component is whatever material your chosen blend specifies.
- Equal-volume bag assumptions should be changed or recalculated if products have different pack sizes.
- This tool does not recommend filler materials or certify a soil recipe.
Frequently asked questions
How much soil fits an 8 by 4 raised bed?
At 16 in of actual fill depth, one 8 × 4 ft bed holds 42.67 ft³ before any settlement allowance.
Are outside bed dimensions correct?
Use inside dimensions because bed walls occupy space.
Does this recommend a 50/30/20 blend?
No. Those are editable example shares; select a blend suitable for your plants and materials.
Read the project guides
- How Much Soil and Compost Does a Raised Bed Need?
Measure internal raised-bed volume, subtract headspace and excluded layers, split a chosen blend into component volumes and round bag quantities accurately.
Calculation method: JICWH methodology. Examples are planning assumptions, not product recommendations.