What this site is
ProjectCalc is a set of free calculators for the materials UK DIY and landscaping jobs are built from: plasterboard, paint, turf, paving, concrete, gravel, topsoil, decking, fencing, flooring and brickwork. Each one takes your measurements and returns a purchasing answer — how many boards, which tins to buy, how many tonnes of sub-base — plus the working behind the headline figure and a shopping list you can read out at the trade counter.
There is no sign-up, no account, no newsletter and no advertising on these pages. You do not have to give us anything to use a calculator, because the calculation happens in your own browser and nothing is sent to us. See the privacy policy for the detail.
Who runs it
ProjectCalc is an independent website. It is not owned or operated by a builder's merchant, a manufacturer or a trade body, and no supplier has any say over what a calculator computes or what these pages say.
The site is also not a shop. We do not sell materials, we cannot take an order, and we cannot give you a price for your job — only quantities, which is the part that is hardest to guess and easiest to get wrong.
Not yet published: the trading details for this site (the name it is operated under, and any registration number) are still being finalised and are not shown here yet. They will appear on this page and on the contact page before the site goes live.
What the calculators do
Every tool follows the same order, because that is the order a job happens in:
- Inputs — metric measurements and UK trade units, either blank-safe or filled in for you.
- Results — one prominent figure first, then the working underneath it.
- Your shopping list — a table of material, quantity and a note on why.
- Check current prices — a clearly-marked placeholder block. There are no live price or affiliate links on this site yet; see the affiliate disclosure.
- Notes and FAQs — the reasoning, the usual UK figures, and the questions people actually ask.
Where the numbers come from
The calculators are built from first principles, not from a table copied off a merchant's website. For each job that means three things:
- The geometry. Areas, volumes and perimeters are worked out from your measurements — a wall run is 2(L + W), a slab is length × width × depth, a post hole is πr²h. Nothing is estimated where it can be calculated.
- A physical constant. Turning a volume into an order needs a density, and turning an area into tins or rolls needs a coverage rate. These are typical UK trade figures: cement at 1,440 kg/m³, sharp sand at 1,600 kg/m³, 20 mm aggregate at 1,500 kg/m³, MOT Type 1 sub-base at 1.8 t/m³, decorative gravel at 1.5 t/m³, screened topsoil at 1.5 t/m³. Liquids and coatings use the coverage printed on the tin you are buying.
- The trade's own allowances. A couple of rules of thumb are baked in that are not pure physics: concrete's dry materials bulk to about 1.54 times the finished volume; dry mortar bulks by about 1.33; and a waste allowance covers cuts and breakages at the rate the job usually needs.
Anything that is a rule of thumb rather than a formula is labelled as an estimate on the page, so you can see which numbers are exact and which are planning allowances. Quantities that can only be bought in whole units — boards, tins, rolls, slabs, bags — are always rounded up, because that is how the merchant will charge you.
How the figures are checked
Each calculator is tested against hand-worked examples before it goes live. The same calculation engine the pages use is run against inputs a person has worked through on paper, and the results are compared figure by figure — the headline number, the working, and the quantities on the shopping list. Bad input is tested at the same time: blank, zero, negative, non-numeric and plainly absurd values must all be caught with a plain-English message rather than producing a confident wrong answer.
The maths is also open to you while you are using it. The arithmetic behind every headline figure is printed under the result, so you can follow it, sanity-check it against your own measurements, and adjust it for the oddities of your own job.
What we will not do
- We will not publish a number we cannot explain. If a page shows a figure, the page also shows where it came from.
- We will not pretend an estimate is a quote. These are planning figures; your merchant's product data and your own measurements come first.
- We will not let a commercial partner influence a calculation or a result. There are no partners today, and the affiliate disclosure sets out the rules if that ever changes.
Corrections
If a calculator gives you a figure you believe is wrong, tell us — a wrong number on a materials site is worse than no number at all. The contact page explains what to include in a message so the problem can actually be reproduced and fixed.