How to measure for block paving
Measure the area to be paved, edge to edge. For a path or a rectangular drive take the length (A) and the width (B). A drive that widens at the gate or turns a corner is usually an L-shape; a splayed entrance can go in as a triangle and a turning circle as a circle. Add another area adds the pieces together.
Think about the edges at the same time. The calculator counts edging kerbs round the full outline of every area you enter. If one side runs along the house or an existing kerb, take those kerbs off the list. If you split one drive into several areas, the edges where they meet are counted too, so use the L-shape where you can.
If you measure in feet and inches, switch the units at the top. The blocks still come out as a count, and the sand and sub-base in tonnes and bulk bags.
Recommended block paving depths
Block paving sits on a laying course of sharp sand over a compacted MOT type 1 sub-base. A path or patio for people needs less sub-base than a drive. These depths come from Marshalls’ installation guides; the buttons apply them to the calculator.
| Use | Sharp sand, laid loose | Type 1 sub-base, compacted | Apply |
|---|---|---|---|
| Path or patioFoot traffic. | 50 mm | 100 mm | |
| DrivewayOrdinary cars. | 50 mm | 150 mm |
The sand goes down loose and damp, is screeded level, and compacts to a noticeably thinner layer once the blocks are vibrated in. That is why the calculator works with the loose depth you spread. Marshalls warns against a compacted laying course much thicker than it recommends, so more sand does not mean a better drive.
Driveway depths are a guide for ordinary cars only. Soft ground, slopes, drainage and heavier vehicles all change the design, so check yours with your supplier or a professional before you dig.
How many blocks per m²?
Standard rectangular blocks measure 200 mm × 100 mm, which is 50 blocks to the square metre. Marshalls’ Bracken driveway pack at Wickes covers its stated area at exactly that rate. Herringbone and basketweave patterns use the same number of whole blocks per square metre; they only change how many are cut at the edges.
The calculator multiplies your area by that figure, adds an allowance for cuts and breakages and rounds up. We suggest 5–10%, and the calculator starts at the top of that range, which suits herringbone, curves and lots of edge cuts; for a straight path in stretcher bond you can move the Extra for cuts and breakages slider down to the lower end. That allowance is our own editorial suggestion; we have not found a UK manufacturer that publishes one. The slider changes the blocks and the edging. The sand, the sub-base and the kiln-dried sand each carry their own allowance, so they stay the same whatever you choose.
Kiln-dried sand for the joints
Once the blocks are laid and compacted, dry kiln-dried sand is brushed into the joints. Thicker blocks have deeper joints, so they take more. Holcim and Marshalls publish how far a 25 kg bag goes and J&T Atkinson gives kilograms per square metre; together they work out at 3.1–4.2 kg/m² for 50 mm blocks, 3.8–5.6 kg/m² for 60 mm and 4.5–7.1 kg/m² for 80 mm. Set the thickness in step 3 and the calculator picks the right rate.
Kiln-dried sand comes in small bags rather than bulk bags, so the list rounds up to whole bags.
Edging kerbs
The calculator can add edging kerbs 200 mm long, the length of a Marshalls Keykerb, which is five to the metre. It measures round the outline of each area, adds the allowance and rounds up. Untick the option if you are edging with something else, or if the paving is held by walls and existing kerbs.
It counts the kerbs only, not anything you bed them on. Ask your supplier what their kerbs need underneath and along the back.
Worked example: a block paved drive
Here is the full calculation for a rectangular drive using the Driveway preset, with standard blocks, edging kerbs all round and our suggested allowance. Every line comes from the same code that runs the calculator above.
- Area 6 m × 4.8 m = 28.80 m²
- Blocks 28.80 m² × 50 per m² + 10%, rounded up = 1,584 blocks
- Laying course: sharp sand 28.80 m² × 0.05 m × 1.7 t/m³ + 10% = 2.69 t
- Sub-base: MOT type 1 sub-base 28.80 m² × 0.15 m × 2.1 t/m³ + 10% = 9.98 t
- Kiln-dried sand 28.80 m² × 3.3 kg/m² + 10% = 105 kg → 5 bags
- Edging 21.6 m of edge + 10% ÷ 200 mm, rounded up = 119 kerbs
On the list:
- 1,584blocks (200 × 100 mm)50 per m² + 10%
- 3bulk bags of sharp sand (approx. 850 kg each)2.69 t needed
- 625 kg bags of sharp sandto top up
- 12bulk bags of MOT type 1 sub-base (approx. 850 kg each)9.98 t needed
- 525 kg bags of kiln-dried sand105 kg for the joints
- 119edging kerbs (200 mm long)21.6 m of edge
Notice where the weight is: the sub-base runs to far more bulk bags than the laying sand, because it is deeper and denser. The kiln-dried sand for the joints is only a few bags. If one side of the drive meets the house or the pavement, take those kerbs off the list.
UK block paving sizes
These are the sizes used by this block paving calculator. UK merchants sell standard blocks by the pack, sharp sand and type 1 in bulk bags of around 850 kg, and kiln-dried sand in bags of 25 kg. Sharp sand also comes in small bags for topping up.
| Product | Size | Good for |
|---|---|---|
| 200 × 100 mm blocks | 200 × 100 mm | The standard rectangular paving block: 50 a square metre. |
| Edging kerb, 200 mm long | 200 mm long | Kerb blocks that hold the edge of block paving. |
| 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. |
Blocks also come in other shapes and sizes. If yours are not standard rectangles, use the coverage printed on the pack: divide your area plus the allowance by the area one pack covers, and round up to whole packs.
Common mistakes when ordering block paving
- Entering the compacted sand depth. The laying course is spread loose and compacts when the blocks are vibrated in. Enter the loose depth.
- Laying the sand too thick. A deeper laying course does not make a stronger drive. Keep to the depth the block maker gives.
- Using the wrong sand. The laying course is sharp sand. Kiln-dried sand is only for brushing into the joints.
- Using path depths for a drive. A drive needs a deeper sub-base. Pick Driveway for cars, and check the design with your supplier.
- Counting edging along walls. The kerbs go round the whole outline. Take off any side that runs along a building or an existing edge.
- Forgetting the block thickness. Thicker blocks need more kiln-dried sand for their deeper joints.
What else you'll need
- Extra sub-base for a wider dig or a path: the type 1 calculator works out MOT type 1 on its own.
- Sharp or kiln-dried sand on its own: the sand calculator handles both.
- Slabs instead of blocks for a patio: the patio calculator does slabs on a mortar bed.
- Gravel for the borders beside the drive: the gravel calculator works it out in tonnes.
- A plate compactor, screed rails and a block splitter or saw for compacting, levelling and cutting.
Last checked 28 October 2026