Sandpit Calculator

Key Takeaways

• The sandpit project calculator lists everything a sandpit build needs from one set of measurements: the play sand, the gravel, the membrane and pegs, the sleepers and screws, and the lid.
• A sandpit needs 300mm of play sand, the minimum depth for children to dig and mould in. A layer of 100 to 150mm is only a safety level for a very young baby, and filling deeper than 300mm is a personal choice.
• Play sand weighs about 1,550kg per m³, so a sandpit filled 300mm deep takes about 465kg of sand for every m², and one 850kg bulk bag of play sand covers about 1.8m².
• A sandpit sits on 100mm of clean 20mm gravel laid under the membrane. One 850kg bulk bag of gravel holds 0.57m³, which covers about 5.7m² at that depth.
• The membrane in a sandpit is overlapped by 100mm at every join and pegged every 500mm along the joins and the edges.
• Sandpit walls stand 100mm above the sand. With 300mm of sand and 200mm sleepers, a sandpit dig is 100mm for a raised frame, 300mm for a half and half pit and 400mm for a sunk pit.
• The long sleepers in a sandpit frame are the inside length plus twice the sleeper thickness, and the short sleepers are the inside width. Each row is turned round on the one below, with two coach screws at every corner.
• A sandpit lid made as two lift-off halves of 18mm exterior plywood, with battens no more than 400mm apart underneath, weighs about 22 to 28kg a half.

The play sand is the part everyone remembers to order. The classic version goes like this: the play sand turns up, the turf is off, and then it dawns on someone that nobody ordered the gravel, or the right screws. A sandpit is a small job, but it is still a build, with a dig, a drainage layer, a frame and a lid. This sandpit project calculator puts the whole build in front of you, from the dig to the lid, before the first spade goes in.

How Does the Sandpit Calculator Work It Out?

The sandpit calculator works as a sandpit volume calculator first, turning your inside length, width and sand depth into m³, then works out every layer.

• Play sand is worked out in kg at 1,550kg per m³, then rounded up to whole 850kg bulk bags.
• The gravel is 100mm of 20mm gravel under the membrane, worked out from the 0.57m³ in each 850kg bulk bag.
• The membrane covers the gravel and runs up the inside of the walls, with 150mm overlaps and a peg every 500mm.
• The sleepers are counted row by row, with the length to cut for each side.
• The lid, if you pick one, is two lift-off plywood halves with their battens and a packer.

Measure inside the walls, because that is the space the sand fills. The extra allowance starts on 10%, and it goes on the sand and the gravel only. Put your own size into the sandpit calculator above to find out exactly how much you need and get an instant price estimate.

How Much Sand Do I Need for a Sandpit?

A sandpit filled 300mm deep needs about 465kg of play sand for every m² of its inside area. That is the sum the sandpit sand calculator does for you: area times depth gives the volume, and volume times 1,550kg gives the weight. A 1.5m by 1.5m pit at 300mm takes about 1,046kg of play sand, or about 1,151kg with 10% extra, which is two 850kg bulk bags. Play sand is sold by weight and a sandpit is measured in metres, which is why a how much sand for a sandpit calculator saves so much guesswork. Our Play Sand comes in 850kg bulk bags, and two are £294.

Which Sand Depth Should You Pick?

A sandpit needs 300mm of play sand, because that is the minimum depth for children to dig and mould in. The 150mm button is there as a safety level for a very young baby, and only for that. You can begin there and add more sand as they get bigger. Going deeper than 300mm is your call, and the 400mm button covers it. Whichever depth you pick, the sand calculator for a sandpit changes the kilos and the bags to match.

How Deep Do I Dig for a Sandpit?

A sandpit dig depends on how you build it: 100mm for a raised frame, 300mm for a half and half pit and 400mm for a sunk pit, with 300mm of sand.

On a raised or half and half pit, the walls stand 100mm above the sand. That gap is what keeps the sand in when it gets dug and flung about. Only sink a pit where the ground drains freely. On clay or damp ground, build it raised.

How Much Gravel Goes Under a Sandpit?

A sandpit takes 100mm of clean 20mm gravel under the membrane, which lets rain drain away below the sand. One 850kg bulk bag of gravel is 0.57m³, so it covers about 5.7m² at 100mm. On a raised or half and half pit the gravel runs under the frame as well, so it covers more ground than the sand does. On a sunk pit it lines the floor of the hole. Our 20mm Gravel comes in 850kg bulk bags at £142 a bag.

How Much Membrane Does a Sandpit Need?

A sandpit needs enough membrane to cover the gravel and run up the inside of the walls, with a 150mm overlap at every join. Peg it every 500mm along the joins and round the edges. The membrane keeps the sand clean and the soil out of it, and it still lets the rain through to the gravel. Our Heavy Duty Weed Membrane comes on a 14m x 1m roll at £15.50.

How Many Sleepers Do I Need for a Sandpit?

A sandpit frame needs two long and two short sleepers in every row, and the wall height decides how many rows you build. Cut the long sleepers to the inside length plus twice the sleeper thickness. Cut the short ones to the inside width, so they fit between the ends of the long ones. On a 1.5m square pit with 100mm thick sleepers, that is two at 1.7m and two at 1.5m in each row.

Turn each row round on the one below, so the long sleepers of the second row sit over the short ones of the first. Fix every corner with two coach screws (heavy wood screws with a hexagon head, driven in with a socket) on every row. Use new UC4 treated softwood or larch, never old creosoted railway sleepers.

What Goes Into a Sandpit Lid?

A sandpit lid works best as two lift-off halves of 18mm exterior plywood, with battens fixed underneath at no more than 400mm apart. A packer screwed along the top of the back wall tips the lid forward at about 1 in 45, so the rain runs off the front. Each half weighs about 22 to 28kg, depending on the plywood. A lid keeps the cats out and the sand dry, and I would not build a sandpit without one. Pick Yes for the lid in the calculator and it adds the plywood, the battens, the packer, the handles and the turn buttons (small swivel catches) to the list.

Next Steps

Measure the sand area inside the walls, pick your build, your depth and whether you want a lid, and the calculator above will find out how much you need and give you an instant price estimate. Click "Click to share this answer" to send the list to whoever is helping you build, or "Save as PDF" to keep a copy.

We sell Play Sand in 850kg bulk bags, 20mm Gravel for the drainage layer and Heavy Duty Weed Membrane on a 14m x 1m roll, with the pegs to hold it down, all delivered nationwide. If you would like to talk with us, call Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.

Have you ever built a sandpit, and did you raise it, sink it or go half and half? We would love to hear how deep you filled it and whether the lid has kept the cats out.

FAQs

How much sand do I need for a sandpit?

Play sand for a sandpit is about 465kg for every m² at 300mm deep, so a 1.5m by 1.5m pit takes about 1,151kg with 10% extra, which is two 850kg bulk bags.

How deep do you dig for a sandpit?

A sandpit dig depends on how you build it. A raised frame needs 100mm, just enough for the gravel layer. A half and half pit needs 300mm: 100mm of gravel plus one 200mm sleeper set into the ground. A sunk pit needs 400mm: 100mm of gravel plus 300mm of sand.

How much gravel do I need under a sandpit?

A sandpit needs 100mm of clean 20mm gravel under the membrane, and one 850kg bulk bag of gravel covers about 5.7m² at that depth.

How high should sandpit walls be?

Sandpit walls should stand 100mm above the sand, so a pit filled 300mm deep needs walls 400mm high above the gravel.

How heavy is a sandpit lid?

A sandpit lid made from two halves of 18mm exterior plywood weighs about 20 to 28kg a half, depending on the plywood, which is enough to stay put in most weather.