Order from measurements
This tool estimates the volume of material for rectangular garden beds. It helps with a new fill or a top-up, and combines different bed sizes into one quantity. All beds share the selected dimension units; each soil depth has its own inches or centimetres setting.
Measure the inside length and width. For a full fill, enter only the depth that will contain the material you are buying. For a top-up, measure the missing layer from the current surface to the desired finished level. Enter the number of identical beds, then add another size if needed.
Bag volume comes from the label. Bags described only by weight cannot be converted accurately without the material density. The optional percentage is a purchasing choice, shown separately from measured volume.
What each input means
| Input | What to enter | Watch for |
|---|---|---|
| Project type | Full fill or top-up. Both count only the layer being added. | For a top-up, measure the gap to the finished level. |
| Inside length and width | Per bed size, in the shared bed units. | Inside dimensions, not the outside of the frame. |
| Added soil depth | The depth of new material, in inches or centimetres per bed. | Not the frame height. |
| Identical beds | How many beds share this size and depth. | Add another bed size for different beds. |
| Bag volume and units | The volume printed on the bag, in ft³ or litres. | Weight cannot be converted without the density. |
| Allowance | An optional percentage added to the order. | A purchasing choice, not a settlement prediction. |
How quantities are calculated
Order volume = base volume × (1 + allowance ÷ 100)
Bags = round up(order volume ÷ bag volume)
Dimensions are converted to one internal unit before multiplication. One cubic foot equals 28.316846592 litres; one cubic yard equals 27 cubic feet. Bag counts use the unrounded total, not the rounded number on screen.
Identical material is pooled across all beds before bags are rounded up. If each bed must be purchased separately, calculate separate orders. The calculator does not select a soil recipe.
Bags, bulk and mixed materials
The result gives the order in cubic feet, cubic yards, cubic metres and litres, and repeats the bag count for other common bag sizes so you can compare what is on the shelf. Loose material is usually quoted by volume: ask whether the supplier’s volume is measured loose or settled, and whether there is a minimum order or delivery charge.
Beds are combined into one order and rounded up once. That is only right when every bed takes the same material. If a new bed gets a different mix from your top-ups, calculate them as separate orders. See a worked soil order.
Full fill and top-up examples
Full fill: 8 × 4 ft × 12 in = 32 ft³ = about 1.185 yd³ or 906.14 L. At 1.5 ft³ per bag, the base quantity needs 22 whole bags. An optional 10% allowance increases the order to 35.2 ft³ and 24 bags.
Top-up: the same bed with a 2-inch missing layer needs 5.333… ft³, about 151.02 L. That is 4 bags of 1.5 ft³ without extra allowance. Two identical beds need 10.666… ft³ and 8 bags in a combined order.
For several beds with different depths, see the worked soil order.
Assumptions & common mistakes
- Use inside dimensions, not the external size of a timber frame.
- Do not count existing soil or lower filler as new material.
- Measure a representative average depth when the surface is uneven.
- Do not assume every soil mix settles by the same percentage.
- Keep compost quantity, soil quality, drainage, and nutrient decisions separate from volume.
The estimate excludes supplier minimums, delivery, compaction modelling, structural loads, and soil testing. Limits: 20 bed-size entries, 100 identical beds per entry, sides up to 100 ft, and added depth up to 10 ft. A zero depth is valid and produces zero volume.
Soil questions
Is topsoil the same as a raised-bed growing mix?
No. A volume result does not establish what a material contains or whether it suits the bed. Check the supplier specification and local guidance; see the filling guide.
Why are bags rounded up?
A partial bag represents material still needed. We divide by the label volume and round up once for the combined order. Base bags and bags with allowance are shown separately.
Does full fill use a different formula from top-up?
No. The distinction helps you measure the correct depth. Both use the depth of new material, not an inferred total bed height.
Should I always add extra?
No universal allowance is assumed. The default is zero. Use an allowance only when your measurements, handling, or supplier advice justify one.