Measure the bed footprint
Record internal length and width in metres (inside the boards).
Soil Calculator
Enter bed dimensions and depth to estimate soil or growing-media volume — with guidance on mixes, drainage and common fill mistakes.
Calculator
Tap a screen and type with the keypad (or your keyboard), choose an option, then press =. The answer shows on the calculator screen, with full details underneath.
Garden Plant Finder
SOIL · GPF
How to measure
Follow these steps for accurate inputs and better results.
Decide fill depth
Vegetables often need 25–40 cm of good growing media.
Allow for settling
Soil settles after watering — order a little extra.
Plan delivery access
Bulk bags are heavy; check where a delivery can be dropped.
Why this matters
Buying the wrong amount of soil is expensive and messy — leftover piles harden, and shortfalls delay planting.
Depth affects root health, drought resilience and yield, especially in raised beds.
A quick volume calculation helps you compare bagged vs bulk delivery costs before you order.
Common mistakes
Too shallow for vegetables
Many crops struggle in under 20 cm of media.
Using only compost
Pure compost can be too rich and unstable — blend with topsoil.
Ignoring drainage
Sealed bases without drainage holes create waterlogged roots.
Filling with garden spoil
Weed-ridden subsoil brings problems into a new bed.
No settling allowance
Levels drop after the first waterings — top up before planting.
Tips from gardening experts
Aim for a blend
A common raised-bed mix is roughly 70% topsoil to 30% compost.
Improve clay carefully
Add organic matter and grit; avoid working clay when wet.
Feed annually
Top-dress with compost each spring to replenish nutrients.
Check pH for specialists
Ericaceous plants need acidic media — don’t use general alkaline topsoil.
Frequently asked questions
How do I calculate soil volume?
Multiply length (m) × width (m) × depth (m). Depth in cm ÷ 100 = metres. Our calculator does this for you.
How many tonnes in a cubic metre of soil?
Roughly 1.2–1.4 tonnes per m³ depending on moisture. We use ~1.3 t/m³ as a planning estimate.
How much soil for a 2×1 m raised bed?
At 30 cm depth: 2 × 1 × 0.3 = 0.6 m³ (about 0.8 tonnes).
Is bagged topsoil the same as bulk?
Quality varies. Bagged is convenient for small jobs; bulk is better value for large beds.
Can I reuse old soil?
Yes if it is free of persistent weeds and disease. Refresh with compost and check structure.
What depth for salad crops?
15–20 cm can work for cut-and-come-again salads; root crops need more.
Do raised beds need a base?
Open bases are best for drainage and worms. Use a liner only where contamination is a concern.
How much compost to mix in?
Often 20–40% by volume for new beds, then annual top-ups.
Why did my new bed sink?
Organic matter and air pockets settle. Top up after a few weeks.
Can I plant straight into new soil?
Yes after watering to settle. For very fresh manure-rich mixes, wait until they have matured.
Sources and further reading
Want more detail? These pages from the Royal Horticultural Society (RHS), the UK’s gardening charity, explain the topic in depth.
Related guides
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Downloads
Soil fill checklist
Measure, order, fill and settle — print before delivery day.
Raised bed soil mix PDF
Simple mix ratios (placeholder download).
Get seasonal gardening advice
See what to sow, plant and prune each month in the Garden Plant Finder seasonal calendar.
Ready to choose plants?
Use Plant Finder filters for soil, sun, wildlife and flowering month — then plan quantities with these calculators.