How to use it
- Measure each bed. Type a rectangle as length × width, and a round bed as circle and its diameter, one bed on each line, in metres.
- Type the Depth of the layer in centimetres.
- Type the Litres in one bag from the bag.
- Read Bags to buy, then open Each bed to see the volume of each bed.
How the volume is worked out
The area of a rectangle is its length times its width. The area of a circle is π times the square of its radius, which is half the diameter. The volume of a bed is its area times the depth, with the depth in metres. The page adds the beds together and turns cubic metres into litres, because one cubic metre is 1,000 litres.
rectangle area = length × width
circle area = π × (diameter ÷ 2)²
volume (m³) = area (m²) × depth (cm) ÷ 100
litres = volume (m³) × 1,000
bags = litres ÷ litres in one bag (rounded up)Bags
The bags are counted in whole bags at the litres you type, rounded up, so you never buy a part bag and run short. Bags of soil, mulch and sand come in different sizes, so read the size on the bag you buy.
What this calculator does not include
- Sloping or shaped beds: measure the area of the top and type the average depth.
- Settling of the soil after it is laid, which can leave a bed lower than the depth you typed.
- The weight of the soil, which the supplier gives for bulk products.
Worked example: a 3 × 1.2 m bed and a circle 1.5 m across, 10 cm deep, in 40 L bags
The rectangle is 3 × 1.2 = 3.60 m². The circle is π × 0.75² = 1.77 m². Together that is 5.37 m² of bed, and at 0.10 m deep it is 0.537 m³, which is 537 litres.
In bags of 40 litres, 537 ÷ 40 = 13.4, so 14 bags are needed.
| Bed | Area (m²) | Litres |
|---|---|---|
| 3 × 1.2 m rectangle | 3.60 | 360 |
| Circle, 1.5 m across | 1.77 | 177 |
| Total | 5.37 | 537 |
Frequently asked questions
How much soil do I need for a raised bed?
Measure the inside of the bed, multiply the length by the width, and then by the depth in metres. Type the size of the bed and the depth in centimetres, and the page gives the cubic metres, the litres and the bags.
How many litres are in a cubic metre?
One cubic metre is 1,000 litres, as the Wikipedia article on cubic metres gives.
How do I find the area of a round bed?
Take the radius, which is half the diameter, square it and multiply by π, about 3.14. Type the bed as circle and its diameter, and the page does this for you.
Why does the page round the bags up?
A part bag cannot be bought, so the page takes the next whole bag. That keeps you from running short of soil when you lay the last part of the bed.
Does the tool store what I enter?
No. The calculation runs in your browser and nothing you type is sent to us or stored.
Sources
Figures and text last checked on Tuesday, November 10, 2026.