Raised Bed Soil Calculator
Calculate how much soil a raised bed needs, and how much compost to blend in.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
Estimate bed volume with a user-entered settling allowance. The 60/30/10 topsoil-compost-aeration split and 1.5 cu ft bag size are planning assumptions, not a universal soil recipe; adjust to plant needs and the supplier’s mix.
Worked example
calculated with the default values below
Bed length 8 ft · Bed width 4 ft · Bed depth 11 in · Number of beds 1 · Settling allowance 10 % Soil needed 32.3 cu ft · Soil needed 1.20 cu yd · Topsoil (60%) 19.4 cu ft · Compost (30%) 9.7 cu ft · Aeration material (10%) 3.2 cu ft · 1.5 cu ft bags needed 22
Method and assumptions
V = L×W×h÷12×N×(1+s÷100); V₁ = 0.6V; V₂ = 0.3V Cubic yards = V÷27. Aeration amendment = 0.1V. Bags = ⌈V÷1.5⌉ (1.5 ft³ per bag). Estimate bed volume with a user-entered settling allowance. The 60/30/10 topsoil-compost-aeration split and 1.5 cu ft bag size are planning assumptions, not a universal soil recipe; adjust to plant needs and the supplier’s mix. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Data sources
The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Disclaimer
These are general gardening estimates. Planting windows, growth, water and nutrient needs vary by place and plant. Check local extension guidance and product labels before acting on an estimate.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
V = L×W×h÷12×N×(1+s÷100); V₁ = 0.6V; V₂ = 0.3V
- L
- Bed length (ft)
- W
- Bed width (ft)
- h
- Bed height (in)
- N
- Number of beds
- s
- Settling allowance (%)
- V
- Soil volume (ft³)
- V₁
- Topsoil volume, 60% (ft³)
- V₂
- Compost volume, 30% (ft³)
Cubic yards = V÷27. Aeration amendment = 0.1V. Bags = ⌈V÷1.5⌉ (1.5 ft³ per bag).
Frequently asked questions
Why does the soil total include a settling allowance on top of volume?
Soil compacts after watering, so the calculator inflates raw volume by the settling percent before reporting it. An 8 by 4 foot bed 11 inches deep holds about 29 cubic feet, but the default 10% allowance lifts the order to roughly 32 cubic feet, or 1.2 cubic yards. The mix then splits that as 60% topsoil, 30% compost and 10% aeration, about 22 bags of 1.5 cubic feet.
Which inputs and limits apply to Raised Bed Soil Calculator?
Use the units shown beside each field. These are form limits, not recommended settings. Bed length: 0.5–100 ft; Bed width: 0.5–50 ft; Bed depth: 2–48 in; Number of beds: 1–50; Settling allowance: 0–30 % V = L×W×h÷12×N×(1+s÷100); V₁ = 0.6V; V₂ = 0.3V Cubic yards = V÷27. Aeration amendment = 0.1V. Bags = ⌈V÷1.5⌉ (1.5 ft³ per bag). Estimate bed volume with a user-entered settling allowance. The 60/30/10 topsoil-compost-aeration split and 1.5 cu ft bag size are planning assumptions, not a universal soil recipe; adjust to plant needs and the supplier’s mix. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
What is a complete worked example for Bed length = 8 ft; Bed width = 4 ft?
Inputs: Bed length = 8 ft; Bed width = 4 ft; Bed depth = 11 in; Number of beds = 1; Settling allowance = 10 %. Calculation: V = L×W×h÷12×N×(1+s÷100); V₁ = 0.6V; V₂ = 0.3V. Results: Soil needed = 32.3 cu ft; Soil needed = 1.20 cu yd; Topsoil (60%) = 19.4 cu ft; Compost (30%) = 9.7 cu ft; Aeration material (10%) = 3.2 cu ft; 1.5 cu ft bags needed = 22.