Raised-bed soil calculator
Work out how much soil/compost mix you need to fill a raised bed, or — if you already have a set amount of mix — how deep it will fill a given footprint.
Result
Soil mix required
Soil mix required
Result
Fillable height
How to use this calculator
- Measure the internal length, width and height of the raised bed.
- Read the volume of soil mix required, or use reverse mode if you already have a fixed amount of mix.
Assumptions
- Assumes a simple rectangular bed with vertical sides — an irregular shape needs a rough equivalent rectangle.
- A 50/50 topsoil-to-compost mix is a common, reasonable fill for most vegetable and flower raised beds.
Technical details: what the fields mean
- Length
length - Internal length of the raised bed.
- Width
width - Internal width of the raised bed.
- Height
height - Internal height (depth) of the raised bed, from the base to the top of the sides.
Methodology
Volume = length × width × height — a straightforward rectangular-box calculation.
Worked example
1.2m × 0.9m bed, 0.3m deep
Inputs: length=1.2, width=0.9, height=0.3
Result: 0.32 m³ (324 L) of soil mix required
Practical guidance
- A 50/50 mix of topsoil and compost suits most vegetable and flower raised beds.
- Fill to just below the top of the sides — soil settles noticeably in the first few weeks.
Common mistakes
- Filling completely to the brim, not accounting for settling, which leaves the bed under-filled a few weeks later.
- Using pure topsoil with no organic matter, which drains and compacts poorly in a raised bed.
FAQs
How much soil do I need for a 1.2m x 0.9m raised bed?
At 0.3m deep, about 324 litres (0.32 cubic metres) of soil mix.
I already have some soil mix — how deep will it fill my bed?
Use reverse mode below: enter your available volume plus the bed's length and width to see the depth it will fill.