About UK Groundworks Calculator

Why this site exists

Most materials calculators give you a volume in cubic metres and leave the rest to you. But you don't order cubic metres: you order bulk bags of Type 1, 25 kg bags of cement, slabs, a membrane and a skip big enough (and legal) for the soil you dig out. This site turns your measurements into that shopping list, and shows the working behind every number.

It's an independent site, built and run by Lewis in the UK. It isn't owned by a builders' merchant, retailer or trade body.

How the numbers are worked out

Every calculator follows common UK practice: compacted Type 1 at 2,100 kg/m³, 25 kg cement bags, bulk bags of about 850 kg, allowances for mortar and concrete shrinking as they're mixed, soil bulking up once it's dug, and UK skip sizes in cubic yards with their weight limits. Each calculator page explains its method under “How we calculate this”, and the small (i) buttons explain terms in plain English.

All the calculations were reviewed in full in October 2026. They're checked by more than 130 automated tests built on worked examples you can redo by hand.

They're estimates for ordering materials, not a structural design. Ground conditions vary, so check anything unusual with a builder or engineer before you start.

How the site is paid for

The calculators are free to use with no sign-up. The site is funded by advertising and by affiliate links: links marked “Ad” go to retailers who may pay a small commission if you buy, at no extra cost to you. Retailers have no say in the quantities, and the results are the same whether or not you use a link. See the privacy policy for details.

Spotted a mistake?

If a figure looks wrong for your job, or there's a calculator you'd like to see, please get in touch or email hello@groundworkscalculator.co.uk. Confirmed errors get fixed, and feedback has already shaped how the calculators work.