Construction calculators
Estimate materials and quantities for building projects.
Estimating materials is about getting the quantity right. Too little means a trip back to the merchant mid-job; too much means material you paid for and have to dispose of. The calculators below turn measurements into an order quantity.
Concrete calculator
Work out how much concrete a slab needs from its length, width, and thickness — in cubic metres, cubic yards, and 25 kg bags, with a waste allowance.
Gravel calculator
Work out how much gravel an area needs from its length, width, and depth — in tonnes and cubic metres, using a bulk density you can adjust.
Tile calculator
Work out how many tiles a floor or wall needs from the area, the tile size, and a waste percentage — with the area and area per tile shown too.
From measurements to quantity
All three calculators do broadly the same thing: they scale an area or a volume and convert it into the unit you actually order in. What differs is what the material weighs and how much waste to allow. That is why the floor area alone is not enough — you also need the depth of the layer.
Why density decides the order
Gravel is rarely ordered by volume. It is usually delivered by weight, and different materials do not weigh the same per cubic metre. Two piles of identical volume can arrive at very different weights and prices. That is why the gravel calculator asks for a density, and the page explains where to find the figure for the material you picked.
Allow for waste from the start
Tiles get cut at edges, in corners, and around pipes, and the offcuts can rarely be reused. So you add a waste percentage. A simple rectangular room needs less than one with alcoves and recesses or a diagonal layout. The waste percentage is a field you set yourself rather than a fixed number, because the right value depends on the room.
Which calculator to use
Concrete calculator turns the volume of a pour into a concrete quantity, whether you mix it yourself or order ready-mix. Gravel calculator goes from area and depth to weight. Tile calculator counts tiles including waste.
If you need the area first, Square footage calculator sits under maths.
What these calculators do not do
They give quantities, not prices, and they do not know your supplier's minimum order or pack sizes. They also take no view on ground bearing capacity, reinforcement, frost protection, or falls to a drain. If the structure itself is in question, that is one for a qualified professional rather than a calculator.
FAQ
- How much waste should I allow on tiles?
- It depends on the room and the layout, not the tile. A square room with straight edges wastes little; lots of corners, recesses, pipe penetrations, or a diagonal pattern wastes noticeably more. Set the percentage to match the room, and round up rather than down — matching the same batch later can be difficult.
- Why do I have to enter a density for gravel?
- Because gravel is delivered by weight while you measure in volume. Density is the bridge between the two. Different aggregates weigh different amounts per cubic metre, so without it the volume cannot become an order.
- Bagged mix or ready-mix concrete?
- It depends on the volume and on how quickly the pour has to be finished. Small amounts are convenient in bags; larger pours become expensive and physically hard to mix by hand, and they need to go in as one continuous pour. The calculator gives you the volume so you can judge which way makes sense.
- What if the area is not a rectangle?
- Split it into rectangles, calculate each one, and add them up. That is far more accurate than averaging a guess, and it rarely takes more than a couple of minutes.
- Do these calculate cost?
- No. They give the quantity in the unit you order in, and the price comes from your supplier. That is deliberate: material prices move constantly and vary locally, so a stale figure would mislead more than no figure at all.
- Do they work in metric and imperial?
- Enter your measurements consistently in one system and read the result in that system. Mixing feet and metres in the same calculation is the most common source of a wrong quantity.