Type 1 is sold by the tonne and laid by the millimetre, and it loses about a fifth of its volume under a wacker. Most calculators handle that badly — several apply the compaction allowance twice and sell you a quarter more stone than the job needs. This applies it once, and shows the arithmetic.
Sub-base for drives, patios, paths and sheds. Enter the area and the finished compacted depth, and get the tonnage to order.
Works in metric and US imperial — you choose at the start and can switch at any time. Every figure this calculator uses is published with its source, and the result comes with a printable order sheet. No account, no email, and nothing you type leaves your browser.
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Type 1 is sold by the tonne and laid by the millimetre, and it loses about a fifth to a quarter of its volume under a wacker. Enter the area and the finished compacted depth; the calculator adds the compaction allowance once and converts at 1,680 kg/m³. Several calculators apply that allowance twice, which is why their answers come out high — order the loose figure here and add nothing to it.
A 5 × 4 m patio sub-base at 100 mm finished is 2 m³ compacted, so about 2.5 m³ loose, weighing roughly 4.2 tonnes. Now the trap: in bulk bags at a declared minimum fill of 800 kg, that is six bags, not four. Bags are where Type 1 jobs go wrong on quantity more than anywhere else.
Not a trade nickname — a specification. SHW Series 800 Clause 803 requires the mixture to meet BS EN 13285 and Table 8/1, with the grading summarised in Table 8/6a: 63 mm at 100%, 31.5 mm at 75–99%, 16 mm at 43–81%. That grading is why it locks up so hard: there is a continuous spread of particle sizes with fines to fill the gaps. The clause itself is set out here.
Multiply area by the finished compacted depth, add about 25% for compaction, then multiply by 1.68 to get tonnes. A 5 by 4 m patio at 100 mm finished works out at roughly 4.2 tonnes. This calculator applies the allowance once, so use the figure it gives without adding to it.
No, and there are two different bags. A bag sold by volume holds about 750 litres; one sold by weight carries a minimum declared fill of 800 kg. Either way you get noticeably less than a tonne, so convert your tonnage into bags rather than assuming one bag equals one tonne.
Type 3 (Clause 805) is the reduced-fines version, made for permeable builds. It drains where Type 1 does not, which is what SuDS and permeable paving require — but it is less stable underfoot and slightly lighter, so the tonnage differs.
Sometimes. Scalpings are cheaper and less consistent: quarry by-product rather than a specified grading, so they vary between loads and between quarries. Fine as a capping layer or under a shed, but not where a specified sub-base is called for.