Car Park Surfacing Calculator — Bays, Sub-base & Markings

A conventional UK parking bay is 2.4m wide × 4.8m long — this is established UK parking-design practice (Manual for Streets, DfT 2007; British Parking Association bay-size guidance), not a single mandated standard. The IStructE recommends moving to a larger 2.6m × 5.0m bay (2023 guidance) to suit modern vehicles. Accessible (disabled) bays are 2.4m × 4.8m with a 1.2m access zone marked alongside (shareable with an adjoining accessible bay) and a 1.2m safety zone at the rear, under BS 8300-1:2018 — about 3.6m total marked width per bay where one access zone applies. As a planning rule of thumb, roughly 65% of total car park area is usable parking (about 15-20 m² gross per space) — the rest is aisles (6m wide for 90° bays), access roads and turning areas. Rough estimate: bays = (Total Area × 0.65) / (2.4 × 4.8).

Sub-base depth depends on traffic loading: light use (cars only) = 150mm, medium (cars + vans) = 225mm, heavy (HGV access) = 350mm or more. Use Type 1 sub-base (crushed limestone/granite) compacted in 150mm layers. A CBR test on the subgrade will confirm the exact depth needed for your site's soil conditions.

Thermoplastic line marking costs approximately £2.50-5.00 per linear metre for standard white or yellow lines. The calculator allows a conservative ~12m per bay (two full lengths + one width), which is an unshared upper bound — in a continuous row each internal dividing line serves two bays, so real consumption is nearer 7-9m per bay once sharing is accounted for. A small allowance is also added for perimeter and aisle markings (an estimating figure, not a derived quantity). Additional markings include disabled symbols, directional arrows, hatching and text. Budget £3-4 per metre for standard markings.

Car parks need surface water drainage falling to channel drains or gullies. For commercial pavements, the minimum longitudinal fall is 1:80 and the minimum transverse (cross) fall is 1:40; tarmac is best laid nearer 1:40 to avoid ponding, while a combined fall of about 1:60 suits smaller private jobs — use our Drainage Fall Calculator for gradients. Linear drainage channels are typically spaced every 15-20m, so channel length depends on your layout — the figure here is a rough allowance from the plot area, not a layout-specific quantity. Under current regulations, car park drainage often needs a petrol/oil interceptor before connecting to the surface water sewer. SuDS solutions ( permeable paving, swales) may be required.

Tarmac is the most common and cost-effective option (£25-45/m²). Block paving is more attractive but costlier (£40-70/m²) and easier to repair. Concrete is durable but expensive (£50-80/m²). Cellular gravel grids offer a permeable option for overflow or low-use areas. For commercial car parks, tarmac with proper sub-base is usually the best value.