UK paving calculator

UK Sub-base Calculator

Last updated 11 July 2026

Estimate compactable granular sub-base for block paving, patios, paths, and drives. Enter the project area and compacted layer depth to get cubic metres, tonnes, and bulk bags.

Quick answer

10 m2 at 100 mm depth needs about 1.10 m3 or 2.20 tonnes of sub-base after 10% allowance.
20 m2 at 100 mm depth needs about 2.20 m3 or 4.40 tonnes.
An 850 kg bulk bag estimate rounds up because partial bulk bags are not orderable.

Interactive estimator

UK sub-base quantity calculator

Imperial Metric

Measurement input Length x width Total area

Project area (m2) Use this when your plan or store project tool already gives total area.

Base depth (mm) Compacted base depth before pavers are installed. Base aggregate density (t/m3) Default is crushed aggregate at 1.6 tons per cubic yard. Waste and compaction allowance (%) Add extra for compaction, uneven excavation, and ordering buffer.

Example area 20 m2 100 mm depth

Order volume 2.20 m3 includes 10% allowance

Order weight 4.40 tonnes 2.0 t/m3 density

Bulk bags 6 850 kg each

Example: 20 m2 at 100 mm needs about 2.20 m3 or 4.40 tonnes, equivalent to 6 x 850 kg bulk bags.

Enter area, compacted depth, density, and allowance to match the project and merchant quote.

UK sub-base estimates

Area	Depth	Cubic metres	Tonnes	850 kg bulk bags
10 m2	100 mm	1.10 m3	2.20 t	3
20 m2	100 mm	2.20 m3	4.40 t	6
30 m2	100 mm	3.30 m3	6.60 t	8
40 m2	100 mm	4.40 m3	8.80 t	11
20 m2	150 mm	3.30 m3	6.60 t	8

Assumes 10% allowance, 2.0 tonnes per cubic metre compactable sub-base, and 850 kg bulk bags.

How to calculate sub-base

Multiply area in square metres by compacted depth in metres, then add an allowance for compaction, trimming, and ordering buffer. For 20 m2 at 100 mm, the compacted volume is 2.0 m3 before allowance and 2.20 m3 after a 10% allowance.

Most UK suppliers quote MOT Type 1 or sub-base by bulk bag, tonne, or loose load. Use the tonnes result for loose deliveries and the bulk bag count for merchant orders.

Choose the right sub-base depth

A pedestrian patio or path often uses around 100 mm of compacted sub-base as a planning depth. Driveways, poor ground, or areas with vehicle loading may need 150 mm or more and should be confirmed locally.

This is a planning estimate, not an engineering specification. Confirm ground conditions, drainage, and product density with your supplier or installer.

Helpful next step

Use the main material estimator for a complete paving order. If your merchant specifies MOT Type 1, use the dedicated product calculator linked below.