Practical tools for measured work
Gravel & Mulch Calculator
Calculate how much gravel, mulch or soil you need for an area and depth.
How it works
How to use it: enter the area's length and width, how deep you want the material spread, and the bag size you plan to buy. The tool converts area × depth into volume and then into a bag count.
Formula. Length and width are in metres and depth is in millimetres, so depth is converted to metres before multiplying:
volume (m³) = length × width × (depth ÷ 1000)
Volume in litres is volume (m³) × 1000, and bags needed is that litre figure divided by bag size and rounded up, since you can't buy a fraction of a bag:
bags = ceil(volume in litres ÷ bag size in litres)
Worked example. With the defaults above (6 m × 3 m area, 50 mm deep, 25 L bags): volume = 6 × 3 × (50 ÷ 1000) = 6 × 3 × 0.05 = 0.900 m³, which is 900 L. 900 ÷ 25 = 36 exactly, so the tool reports 36 bags with nothing left over. 0.9 m³ is also about 0.9 × 1.30795 ≈ 1.177 yd³.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Length
- 6 m
- Width
- 3 m
- Depth
- 50 mm
- Bag size
- 25 L
Primary result: Volume: 0.900 m3.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
This is a loose-fill geometric estimate - it doesn't model compaction. Gravel, mulch and soil settle and compact differently by material, so the volume you spread loose is not the same as the volume once it's settled or walked on; ask your supplier for a compaction or coverage factor for your specific material.
It also assumes a flat, rectangular area at a uniform depth - it doesn't account for slopes, irregular shapes, edging that displaces material, or extra depth needed at the edges of a bed. Bagged material coverage varies by product density, so confirm the actual volume per bag with the label or supplier rather than assuming a round number.
Frequently asked questions
Should I buy exactly the number of bags this shows?
Treat it as a minimum. Bag volumes are nominal and material settles in the bag and on the ground, so buying a little extra avoids a second trip for a small top-up, especially on irregular or sloped areas.
Does this work for bulk (loose, non-bagged) material too?
Yes - the cubic metre, cubic yard and litre figures are the volume you need regardless of how it's sold. Only the "Bags" result depends on the bag size field; ignore it if you're ordering bulk by the tonne or cubic yard.
Why is the cubic yard figure not a round number?
Cubic yards and cubic metres aren't related by a round conversion factor - 1 m³ is about 1.30795 yd³ - so converting a tidy metric volume rarely lands on a tidy yard figure.
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