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 run the whole way from measurements to what you actually have to buy.
Concrete calculator
Work out how much concrete a pour needs — the raw volume, the order volume with your own allowance, and the whole bags, in metric or US units.
Gravel calculator
Work out how much gravel an area needs — the volume, and the weight in both metric tonnes and US short tons, from a bulk density you control.
Paint calculator
Work out the paintable area of a room, how much paint the coats will use, and how many whole tins to buy — in metric or US customary units.
Tile calculator
Work out how many tiles a floor or wall needs from the area, the tile size and a waste allowance — then how many whole boxes that is, and what is left over.
Measurements, then quantity, then purchase
Every calculator here follows the same three steps. Measurements first: length, width and either a thickness or a wall height. Then the quantity the job consumes: a volume, a weight, a tile count, a number of litres. Then the purchase, which is the step people skip — bags, boxes and tins are indivisible, so what you buy is always a rounded-up version of what you use, and the difference is worth seeing before you pay for it.
Each one switches between metric and US customary units. Switching converts the numbers rather than relabelling them, so the same slab, the same floor and the same room survive the change — only the figures on screen move.
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, offers a few figures from a public highway table, and asks you to say whether that density describes loose or compacted material. It does not convert between the two: how far an aggregate consolidates depends on the material, the moisture and the plant, and no single multiplier covers it.
The weight is reported both in metric tonnes of 1,000 kg and in US short tons of 2,000 lb. They are different units, and the roughly ten percent between them is easy to miss on a delivery note.
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.
There is a second kind of extra underneath it, and the two are worth keeping apart. Tiles come in whole boxes, concrete in whole bags and paint in whole tins, and the last one is rarely empty when the job is done. The waste allowance is a margin you choose; the surplus from rounding up to a whole pack is one the shop imposes on you. Each calculator reports them separately, so you can see whether a different pack size shrinks the leftovers.
Which calculator to use
Concrete calculator shows the raw pour, the order volume with your own allowance, and the whole bags that follow from the yield printed on the bag. Gravel calculator goes from area and depth to a weight in both metric tonnes and US short tons. Tile calculator counts tiles including waste and turns them into whole boxes. Paint calculator takes a room's walls, deducts the doors and windows, and works out the tins.
If you need the area first, Square footage calculator sits under maths.
What these calculators do not do
They give quantities, not market prices, and they do not know your supplier's minimum order. They know your pack sizes only because you type them in: the yield per bag, the tiles per box and the tin size are fields you fill from the packaging, not a product database. The paint calculator will multiply a price per tin you enter, but nothing here looks a price up or converts a currency. 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 US units?
- Yes. Each calculator has a unit switch, and switching converts every measurement rather than relabelling it, so the job stays the same size. Concrete and gravel also report cubic yards alongside cubic metres, and gravel gives both metric tonnes and US short tons. Paint says "US gallon" rather than "gallon", because the imperial gallon is about a fifth larger.
- Why can't I just scale up the weight on the bag?
- Because a 25 kg bag of dry mix does not make 25 kg worth of concrete volume. The water fills the voids between the grains, so the mixed material takes up less room than the dry ingredients. The figure you need is the yield — how many litres or cubic feet of wet concrete one bag makes — and it is on the bag or its data sheet. The calculator asks for exactly that, with a few documented values as a starting point.