Measure the surface
For a rectangle, multiply length by width. For a circle, use π × radius². Add separate beds that will receive the same material; their volumes are combined before bags are rounded up.
03 / Beds & borders
Soil and mulch calculator
Calculate soil, mulch or gravel volume for garden beds, then compare bags with cubic metres or cubic yards.
Know what goes into your estimate
From garden bed to bag count
Small measurements. Useful numbers.
Choose your depth
Multiply each area by its desired material depth, using consistent units. The example depth is an editable measurement, not a planting recommendation. Match the depth to your project and material.
Compare bags and bulk
One cubic metre equals 1,000 litres. Divide litres by your bag volume and round up to complete bags. Bulk suppliers may use cubic metres or cubic yards and their own minimum increments.
How many 50 L bags for a garden bed?
Examples use a 4 × 2 m rectangular bed and no extra allowance. Depths illustrate the arithmetic; choose the depth appropriate to your material and project. Adding an allowance increases the volume before bags are rounded up.
| Bed depth | Volume | 50 L bags |
|---|---|---|
| 50 mm | 0.4 m³ / 400 L | 8 |
| 75 mm | 0.6 m³ / 600 L | 12 |
| 100 mm | 0.8 m³ / 800 L | 16 |
| 150 mm | 1.2 m³ / 1,200 L | 24 |
These are examples, not product specifications. Enter your own measurements and product details in the calculator above.
Common questions
How much mulch covers a 4 m × 2 m bed at 75 mm?
The volume is 4 × 2 × 0.075 = 0.6 m³, or 600 L. With no extra allowance, that is twelve 50 L bags. With 10% extra, the estimate is 660 L, rounded up to fourteen 50 L bags.
Can I use this for soil and gravel too?
Yes, the geometric volume is calculated in the same way. Choose the material label for your shopping list. The tool does not convert volume into kilograms or tonnes because density, moisture and compaction vary.
What if my bed has an unusual shape?
Break it into rectangles and circles where appropriate, without overlapping their areas. For changing depths, model separate sections. An average depth is only useful if it fairly represents the actual surface.
How are feet, yards and inches handled?
Imperial bed lengths use feet and depth uses inches. Bags use cubic feet, while the bulk result uses cubic yards. There are 27 cubic feet in one cubic yard. Metric depth uses millimetres, not centimetres.
Where does the volume method come from?
The area-times-depth method and cubic-foot to cubic-yard conversion are described by Iowa State University Extension. This calculator follows that geometry while leaving depth and allowance choices to you.