Topdressing calculator

Volume is easy, weight is not

The volume part is simple: area times depth, and a hundred square metres at ten millimetres is exactly one cubic metre. That never changes.

Weight does. Dry washed sand runs about a tonne and a half to the cubic metre, a damp sandy loam more, and a light organic mix considerably less. That is why the density here is a field you can change rather than a constant baked in: the number that matters is your supplier's, particularly if a trailer or a ute tray has a limit you need to respect.

Thin, and twice

The common mistake is going deep to fix a bumpy lawn in one weekend. Grass has to grow back through the dressing, and leaf that is buried does not photosynthesise. Two thin passes a month apart level better than one thick one, and the lawn stays green throughout.

Spread it with the back of a level lawn rake or a drag mat, working it into the low spots rather than smoothing it flat across the top. The aim is to fill hollows, not to raise the whole surface.

Questions people ask

How much sand do I need to topdress my lawn?

Area times depth. A hundred square metres at 10 mm is one cubic metre, which is roughly 1.5 tonnes of dry washed sand. Bagged product is sold by volume, so a cubic metre is about twenty-five forty-litre bags.

How deep should topdressing be?

Thin enough that the grass still shows through when you have finished, typically 5 to 10 mm over a healthy lawn. Levelling a hollow can take more in that spot, but burying leaf across the whole lawn sets it back rather than helping it.

How much does a cubic metre of sand weigh?

Around 1.5 tonnes dry, and more when damp, which is why this page asks rather than assumes. Suppliers will give you the figure for what they are actually selling, and it matters when a trailer has a load limit.

When should I topdress?

When the grass is growing strongly enough to grow back through it, which for warm season lawns means the warm months and for cool season lawns means spring or early autumn. Topdressing a dormant lawn just smothers it.

Sand or a soil mix?

Match what is already there. Straight sand over clay builds a layer that water sits on top of, which causes the problem it was meant to fix. If you are levelling rather than changing the soil, a mix close to your own soil is the safer choice.