MOT Type 1 Calculator

MOT Type 1 sub-base for patios, paths and driveways: tonnes for your area and depth, and how many 25 kg or 850 kg bulk bags to order.

MOT Type 1 is the standard sub-base in the UK: crushed stone or recycled concrete graded from about 40 mm down to dust, made to the Highways specification. The fines fill the gaps so it compacts into a hard, load-bearing layer under patios, paths, driveways and shed bases. Merchants sell it in 25 kg bags, 850 kg bulk bags and loose by the tonne. Type 1 compacts considerably, so this calculator adds 20% to the finished volume by default. Enter the area and the compacted depth and it gives the tonnes and m³, and the bags or bulk bags. As a guide, a tonne covers about 4.5 m² at 100 mm compacted.

Units

Bag sizes

Material

Area

Shape

Length

Width

Depth

Density (tonnes per m³)

t/m³

Extra for waste and compaction

Bag size

Compacts to roughly 2.1 tonnes per m³, which the 20% extra allows for.

Weight: 2.59 tonnes
Volume: 1.44 m³
Bags: 104

Bags needed by size
25 kg bag	104
850 kg bulk bag	4

Price (optional)

Price is per

How it was worked out

Area: 4 m × 3 m = 12 m²; × 100 mm (0.1 m) deep = 1.2 m³
Plus 20% extra = 1.44 m³
1.44 m³ × 1.8 t/m³ = 2.59 tonnes (2,592 kg)
2,592 kg ÷ 25 kg per bag = 103.7, rounded up to 104 bags

Typical weights of common materials

Material	t/m³	tons/yd³	lb/ft³
Concrete	2.40	2.02	150
Gravel	1.60	1.35	100
Pea gravel	1.60	1.35	100
Crushed stone / crushed rock	1.60	1.35	100
River rock	1.50	1.26	94
Landscape rock / pebbles	1.50	1.26	94
Crushed limestone	1.60	1.35	100
Decomposed granite	1.50	1.26	94
Crusher run	1.60	1.35	100
Road base	1.70	1.43	106
Crusher dust	1.50	1.26	94
Aggregate (20 mm)	1.60	1.35	100
All-in ballast	1.65	1.39	103
MOT Type 1 sub-base	1.80	1.52	112
Sand	1.60	1.35	100
Topsoil	1.30	1.10	81
Garden soil	1.30	1.10	81
Fill dirt	1.40	1.18	87
Mulch	0.35	0.29	22
Bark chippings	0.30	0.25	19
Asphalt (compacted)	2.32	1.96	145

Loose, as-delivered figures; asphalt and concrete are as laid. Moisture, stone size and source change the real weight, so use your supplier's figure when you have it. Tons are US short tons (2,000 lb).

Common use cases

A sub-base for a patio or paving slabs
A driveway base for block paving or tarmac
A firm, level base for a shed or garden building
Paths and hard standing

How to use

Choose feet and inches or metres and millimetres, and the country whose bag sizes you want.
Enter the length and width of the area, or switch the shape to a circle, triangle or a known area. Use Add another area for L-shapes and separate beds.
Enter the depth of Type 1. Enter the compacted depth: commonly 100 mm for patios and paths, 150 mm or more for driveways.
Check the density and the extra allowance. Change the density if your supplier quotes a different figure.
Read the volume, weight and bag count, and add a price per ton, cubic yard, m³ or bag for a cost estimate.

FAQ

How much Type 1 do I need for a patio?

A 4 × 3 m patio with 100 mm of compacted Type 1 needs 1.2 m³ finished. With 20% extra at 1.8 tonnes per m³ loose, that's about 2.6 tonnes: just over three 850 kg bulk bags, so order four.

How deep should Type 1 be?

About 100 mm compacted for patios and paths, and 150 mm or more for driveways, more on soft or clay ground. Lay and compact it in layers with a plate compactor rather than all at once.

How much does a tonne of Type 1 cover?

About 4.5 m² at 100 mm compacted, or about 3 m² at 150 mm, using this calculator's figures. An 850 kg bulk bag covers about 4 m² at 100 mm.

What's the difference between Type 1, Type 3 and scalpings?

Type 1 has fines and compacts into a dense, strong layer. Type 3 has fewer fines so water drains through it, which suits permeable paving. Scalpings are a cheaper, less consistent mix of stone and soil, often used for tracks and under less demanding surfaces.