How to measure for sand
Measure the area the sand will go under: for block paving or a patio, that is the paved area. Take the length (A) and width (B) of a rectangle, or split the area into rectangles, triangles, circles and L-shapes and add each with Add another area. If you measure in feet and inches, switch the units at the top.
For a layer of sand, the depth is the thickness as you spread it. Sharp sand under block paving is screeded loose and then compacts as the blocks are vibrated into it, so enter the loose depth from the paving maker’s instructions, not the finished one. For a patio, the depth is the thickness of the bed under the slabs.
Kiln-dried sand for the joints works differently. It is brushed in after the blocks are laid, and how much you need depends on the depth of the joints, which is set by the thickness of the blocks. Tick Add kiln-dried sand for block paving joints and choose the block thickness: the calculator uses a rate per square metre instead of a depth.
How much sand: typical depths and rates
These are the figures UK paving manufacturers and suppliers give for the jobs sand is most often bought for. Set the depth in step 2 and the jointing sand in step 3 to match.
| Use | Sand | Depth or amount | Apply |
|---|---|---|---|
| Block paving laying courseScreeded loose, compacts with the blocks | Sharp sand | 50 mm before compaction | |
| Patio bed under slabsMixed with cement | Sharp sand | 30–60 mm bed | |
| Joints of 50 mm blocks | Kiln-dried sand | 3.1–4.2 kg/m² | |
| Joints of 60 mm blocks | Kiln-dried sand | 3.8–5.6 kg/m² | |
| Joints of 80 mm blocks | Kiln-dried sand | 4.5–7.1 kg/m² |
The jointing figures are ranges because block shapes and joint widths differ. The calculator uses J&T Atkinson’s rate for each block thickness; the bag coverage that Holcim and Marshalls publish makes up the rest of the range. The laying course goes on a compacted sub-base, which the type 1 calculator works out.
How much sand for block paving?
Block paving takes two kinds of sand. Under the blocks goes a laying course of damp sharp sand, which Marshalls says to spread 50 mm deep before compaction. Over the top goes kiln-dried sand, brushed into the joints so the blocks lock together. Use sharp sand for the laying course, as the paving makers specify, not soft building sand.
On a path or patio, the laying course is by far the bigger order, usually in bulk bags, while the jointing sand comes to a few small bags. The worked example below shows both. For the blocks, edging and sub-base as well, use the block paving calculator.
How much sand for patio slabs?
Most patios are laid on a full bed of sharp sand mixed with cement, 30–60 mm thick. Marshalls’ installation guides use the thinner part of that range, while Wickes and B&Q suggest a thicker bed. Enter the bed depth you are using and the calculator gives the sharp sand for it.
A patio bed also needs cement, so for the full mix use the sand and cement calculator, which works out both from the mix ratio. The patio calculator does the slabs.
Which sand do you need?
The sand you choose in step 2 sets the density, so the weight follows the sand you actually buy.
Sharp sand calculator
Sharp sand, also sold as grit sand, is coarse and gritty. It is the sand for block paving laying courses, patio beds and concrete, and it weighs typically 1.6–1.8 t/m³ loose. Pick Sharp sand (grit sand) in step 2; it is the default.
Building sand calculator
Building sand, or soft sand, is finer and smoother, typically 1.6–1.7 t/m³. It makes a workable bricklaying mortar, but paving makers specify sharp sand for laying courses and patio beds. For a wall, the amount depends on the bricks or blocks rather than an area, so the mortar calculator is the better tool.
Kiln-dried sand calculator
Kiln-dried sand is fine, dry sand that flows into narrow joints. It comes in small bags only and is bought by the square metre of paving, not by depth. Thicker blocks have deeper joints, so a bag goes much further on thin blocks than on thick ones. Sand is also brushed into some artificial grass as infill; the artificial grass calculator works out that amount.
Worked example: sand for a block paved patio
Here is the full calculation for a rectangular block paved patio: sharp sand for the laying course at the default depth, plus kiln-dried sand for the joints of 50 mm blocks, with the suggested extra allowance. Every line comes from the same code that runs the calculator above.
- Area 5 m × 3 m = 15.00 m²
- Volume of sharp sand 15.00 m² × 0.05 m (50 mm) = 0.750 m³
- Weight of sharp sand 0.750 m³ × 1.7 t/m³ = 1.275 t (1,275 kg)
- Plus extra 1,275 kg + 10% = 1,403 kg (1.40 t)
- In bulk bags 1,403 kg ÷ 850 kg = 1.65, rounded up = 2 bulk bags
- Jointing sand 15.00 m² × 3.3 kg/m² + 10% = 54 kg → 3 bags
On the list:
- 2bulk bags of sharp sand (approx. 850 kg each)1.40 t needed
- 325 kg bags of kiln-dried sand54 kg for the joints
Notice the difference in scale. The laying course is a bulk-bag order, but the jointing sand is a handful of small bags, because it only fills the narrow gaps between blocks. Keep any leftover kiln-dried sand somewhere dry: joints usually need topping up once the sand has settled in.
UK sand bag sizes
Sharp sand and building sand are sold by weight, in bulk bags and in small bags of 25 kg. Kiln-dried sand comes in small bags only. Turnbull’s buyers’ guide notes that bulk bags of sand are a nominal weight and vary from bag to bag, so treat the weight as approximate.
| Product | Size | Good for |
|---|---|---|
| Bulk bag, 850 kg | 850 kg | The most common merchant bulk bag. About 10 m² of gravel at 50 mm. |
| Small bag, 25 kg | 25 kg | Merchant “handy bag” or trade pack. |
Some merchants list sand bulk bags by volume as well as weight. If yours only gives a volume, multiply it by the density to compare, or ask for the weight.
Common mistakes when ordering sand
- Buying building sand for a laying course. Paving makers specify sharp sand under blocks and slabs. Soft sand is for mortar.
- Entering the compacted depth. The laying course compacts when the blocks are vibrated in. Enter the loose depth or you will run short.
- Forgetting the jointing sand. It is a separate product, sold in small bags. Tick the jointing option so it goes on the list.
- Choosing the wrong block thickness. Thicker blocks have deeper joints and take more kiln-dried sand per square metre.
- Leaving kiln-dried sand out in the rain. It only flows into the joints when it is dry. Keep the bags under cover until you brush it in.
- Forgetting the cement for a patio bed. A patio bed is sand and cement, not sand alone.
What else you'll need
- Blocks, edging and a sub-base for block paving: the block paving calculator does the whole job.
- Cement for a patio bed: the sand and cement calculator works out the sand and cement together.
- A compacted type 1 sub-base under the sand: use the type 1 calculator.
- Slabs for a patio: the patio calculator covers them.
- A plate compactor, screed rails and a straight edge for the laying course, plus a soft brush for the jointing sand.
Last checked 28 October 2026