Sri Lanka Interlock Paving Calculator

Interlock (interlocking concrete block) paving is the standard finish for home driveways, carports and garden paths across Sri Lanka. This calculator turns a paved area into an order quantity you can hand to an interlock supplier, using the nominal block sizes in SLS 1425 (the Sri Lanka Standards specification for interlocking concrete paving blocks) and the bedding and jointing practice published by the Interlocking Concrete Pavement Institute (ICPI). Every figure is deterministic:

1. Paved area A (m²). If you enter dimensions, A = length × width. If you enter a direct area, it is used as-is.
2. Base block count. blocks = A × blocks/m², rounded up to a whole block. A rectangular 200 × 100 mm paver covers 0.02 m², so it needs 50 blocks/m² — a figure you can verify from the block size itself (1,000,000 mm² ÷ 20,000 mm² = 50). I-shape and zig-zag blocks are typically ~40/m² and hexagons ~25/m². These are manufacturer defaults and every one is editable, because coverage varies by supplier.
3. Wastage. total = ceil(blocks × (1 + wastage/100)). ICPI guidance is roughly 5% for straight or stack-bond laying and 10% for herringbone or 45° work, which cuts more blocks at the perimeter.
4. Bedding sand. volume = A × (bedding mm ÷ 1000), for the compacted sand layer that sits directly under the blocks (ICPI range 25–50 mm; 40 mm default). The result is shown in cubes (1 cube = 100 ft³ = 2.832 m³) and cubic feet — the units Sri Lankan hardware stores sell sand in.
5. Jointing sand. A practical allowance of about one 25 kg bag of fine sand per 10 m² of paving, swept into the joints, shown as ceil(A ÷ 10) bags. This is a rule of thumb, not an SLS figure.
6. Optional cost. Blocks × your per-block price, plus bedding sand cubes × your per-cube price, totalled in rupees. It only appears when you enter a price, because block prices vary by shape, colour and supplier.

Block thickness never changes the count — a block covers the same plan area at 60 mm or 80 mm. Thickness is a strength choice: SLS 1425 uses 60 mm for pedestrian and light use and 80 mm for vehicular traffic such as driveways. The tool surfaces this as guidance so you pick the right class, without inflating the block quantity. Sub-base (hardcore) depth and edge restraint are out of scope: the sub-base is a geotechnical decision, and the edge restraint is reminded but not quantified in this version.

• Sri Lanka Standards Institution — SLS 1425: Interlocking concrete paving blocks
• Interlocking Concrete Pavement Institute (ICPI) — segmental paving tech specs
• CIDA Sri Lanka — construction material and estimating references

Block coverage defaults and thickness classes were last cross-checked against SLS 1425 nominal sizes and ICPI guidance on 2026-07-17. Blocks per m² varies by supplier — always confirm against your product sheet before ordering.