Construction Calculators

One Sum, Three Different Things to Worry About

All three run the same arithmetic. Area is length times width, or π times the radius squared if it is round. Volume is area times depth. Everything after that is unit conversion — cubic feet into cubic yards by dividing by 27, cubic centimetres into litres by dividing by a thousand. Nothing about that changes between stone, bark and resin.

What changes is what goes wrong at the wrong depth, and the three fail in three different directions. With aggregate the risk runs one way: too thin and the stones never lock together, so the surface scatters under a tyre. Mulch has a limit at both ends — too thin and weeds come through, too thick and the bed underneath is starved of water and air. Epoxy is the odd one out, because its limit is chemical rather than physical: it cures by generating heat, and a deep pour holds that heat in rather than shedding it, so past a certain thickness the casting can crack, yellow or scorch regardless of how carefully it was measured.

That is why each calculator says something different about depth. The same multiplication, three distinct judgements wrapped around it.

Ordering by Volume, Buying by Weight, Bag or Kit

Volume is what a project needs, but it is rarely what appears on an invoice. Aggregate is weighed on a weighbridge and quoted in tons, which puts density between your calculation and your order. Mulch is light enough that weight barely features, and is sold by the bag or the cubic yard instead. Resin is sold as a kit of two bottles that have to be combined in a fixed proportion, so the figure that matters is not one quantity but two.

So the gravel calculator treats density as an editable input and states the figure it used, the mulch calculator works in bags and tells you how many fit in a cubic yard, and the epoxy resin calculator splits the total into resin and hardener at your kit's own ratio — by weight or by volume, which for epoxy are two different numbers for the same mix. Each reports in the unit its own trade quotes in, rather than forcing all three into the same column.

Measure the Site Once, Order Twice

Most garden projects need both of the landscaping tools. A new path is stone down the middle and bark either side of it; a parking area often ends at a planted border. The efficient way to handle that is to walk the site once with a tape, write down every rectangle with a note of what is going in it, and sort the list afterwards.

Keep the lists separate rather than totalling a single area figure, because the depths differ and the materials come from different suppliers in different units. Two tidy lists beat one combined number you then have to unpick at the merchant's counter.

The same discipline applies to a resin project for a different reason. A river table is usually two calculations rather than one — the channel between the slabs, and then a thin flood coat across the whole finished surface — and they are not interchangeable. Measuring the tabletop when you meant the channel is the most expensive mistake in that craft, because the top is several times the area of the river running through it.

Where measurements arrive in a mix of metres and feet, the unit conversion calculator will square them up before you start, and the mixed number calculator turns a depth read off a tape in eighths into the decimal these tools expect.