Raised Bed Soil Calculator — Garden Bed Volume
Find out exactly how much soil mix you need to fill a rectangular raised garden bed. Enter the bed dimensions, choose your unit system, and get the volume in cubic feet or cubic metres plus an estimate of how many bags to buy.
Unit system
ft
ft
in
Volume of soil mix required to fill the raised bed to the specified depth
- 1
Depth in feet
12 in ÷ 12 = 1 ft - 2
Soil volume
4 × 2 × 1 = 8 ft³
How does this calculator work?
Raised bed soil volume = Length × Width × Depth (all in consistent units). A standard 4 × 8 ft bed with 12 inches of fill needs 32 cu ft ≈ 16 two-cubic-foot bags ≈ 906 litres ≈ 1 040 kg of dry mix. Add 10–15% for settling after watering.
Formula
How this is calculated
The volume of a rectangular raised bed is simply length × width × depth — the same formula as for any rectangular prism. The only subtlety is keeping units consistent: if length and width are in feet, depth must also be in feet (convert inches by dividing by 12 before multiplying). In metric, convert centimetres to metres by dividing by 100.
The dry-mix density used to estimate mass is 1 150 kg/m³ (about 72 lb/ft³), a midpoint representative of a typical commercial raised-bed mix of topsoil, compost and perlite. Bags of soil mix sold at garden centres are usually 50-litre (metric) or 2-cubic-foot (US imperial); the calculator divides the total volume by these amounts and rounds up to the nearest bag. Actual bag counts depend on the product — check the bag label for its stated coverage.
Vegetables with shallow roots (lettuce, herbs) do well in 15–20 cm (6–8 in) of soil. Most vegetables need 30 cm (12 in). Deep-rooted crops such as carrots, parsnips and tomatoes benefit from 45 cm (18 in) or more. Add 10–15% extra volume to allow for settling after the first watering.
Frequently asked questions
Most vegetables grow well in 30 cm (12 in) of soil. Shallow-rooted crops like lettuce and herbs can manage 15–20 cm; deep-rooted crops such as carrots and tomatoes benefit from 45 cm or more. The deeper the bed, the fewer problems with compaction and drainage.
Divide the total volume by the bag size. In the US, bags are usually 1–2 cu ft (28–57 L); in metric countries, 50-litre bags are common. The calculator estimates bag count using 2 cu ft (US) or 50 L (metric) and rounds up. Check the coverage stated on the bag label for accuracy.
A common recommendation is the "Mel's mix": ⅓ compost, ⅓ peat moss or coco coir, ⅓ coarse perlite or vermiculite. This provides good drainage, aeration and fertility. Avoid pure topsoil — it compacts badly in a raised bed. Amend with compost each season.
Also known as
TG we-Calculate Editorial Team. (2026). Raised Bed Soil Calculator — Garden Bed Volume [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/raised-bed-soil-calculator
TG we-Calculate Editorial Team. "Raised Bed Soil Calculator — Garden Bed Volume." TG we-Calculate. 2026. https://we-calculate.com/calculator/raised-bed-soil-calculator.
TG we-Calculate Editorial Team, "Raised Bed Soil Calculator — Garden Bed Volume," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/raised-bed-soil-calculator
@misc{wecalculate_raised_bed_soil_calculator, title = {Raised Bed Soil Calculator — Garden Bed Volume}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/raised-bed-soil-calculator}}, year = {2026}, note = {TG we-Calculate} }
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