Raised Bed Soil + Compost Ratio Calculator

How to use the raised bed mix calculator

Choose rectangle or circular bed shape, enter length, width (or diameter), and depth in inches. Set your target compost percentage and preferred output units (cubic feet, cubic yards, or liters).

Results show total volume plus separate soil and compost quantities based on your ratio.

Volume and ratio formulas

Rectangle volume (cu ft) = Length × Width × (Depth in ÷ 12). Circle volume = π × Radius² × (Depth in ÷ 12).

Compost volume = Total volume × (Compost % ÷ 100). Soil volume = Total volume − Compost volume. Cubic yards = Cubic feet ÷ 27.

• Common compost ratios: 25–40% for vegetable beds
• Many gardeners use 30% compost as a balanced starting point
• Convert to liters: cubic feet × 28.3168

Worked example

An 8 ft × 4 ft raised bed filled to 12 inches deep with a 30% compost mix: Total volume = 8 × 4 × 1 = 32 cubic feet.

Compost needed = 32 × 0.30 = 9.6 cu ft. Soil or soil blend = 32 − 9.6 = 22.4 cu ft (about 0.83 cubic yards of each component combined).

Building a balanced raised bed mix

Compost supplies organic matter and nutrients; topsoil or a soil blend provides structure and mineral content. Very high compost percentages can shrink and settle faster than balanced mixes.

Many growers combine compost with topsoil, peat-free coir, or aeration additives like perlite for drainage in root crops and herbs.

Planning purchases

Order 10–15% extra to account for settling during the first season. Mix components thoroughly before filling the bed, and water once to settle before final top-off.

• Use finished, screened compost — avoid hot or unfinished material.
• Test soil pH after mixing if growing acid-sensitive crops.
• Top off beds in year two as organic matter decomposes.
• See our topsoil and mulch calculators to cross-check bulk orders.