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Measuring the way you actually measure

Every tool accepts metric or imperial input, and imperial can be typed as you would say it — 12'6" is twelve feet six inches, no decimal conversion needed. Mixed units are fine too: a wall measured in metres and a door in centimetres will be reconciled before anything is calculated.

Concrete

Volume is length by width by depth, but the shape matters. The calculator handles rectangular slabs, circular footings and post holes, and sums several of each so a run of fence posts is one calculation rather than twelve. Output is in cubic metres and cubic yards, then converted into a bag count for standard pre-mixed bag sizes, using the yield printed on the bag rather than the dry weight. A waste allowance is added by default because sub-bases are never perfectly level and a short pour means a cold joint; the allowance is a visible input, not a hidden fudge.

Paint

Coverage starts from wall area — the perimeter of the room times the height — minus openings. Doors and windows are entered separately and subtracted, because on a small room they are a meaningful share of the wall. The result is multiplied by the number of coats and divided by the coverage rate per litre, which varies by paint and by surface; the default is a typical emulsion figure and the page says so, so you can substitute the number from the tin. The tin count rounds up to whole tins of a size you choose, which is the figure you take to the shop.

Gravel, sand and mulch

Bulk material is priced by the tonne or the cubic metre and bought by the bag or the trailer load, so the gravel and mulch calculators give all of those from one set of dimensions. Each material has a loose bulk density on the page — crushed rock, sand, road base, bark mulch, compost and topsoil are all different — and the depth field reads its own unit, so 75mm and 3in are both understood.

Flooring, decking and fencing

These count pieces rather than volume. The flooring calculator divides the room by the tile or plank size and ties the waste to the laying pattern, 10% straight, 15% diagonal and 20% herringbone. Decking counts rows across the deck, turns them into lineal metres and boards, and adds joists and screws. Fencing counts bays, then posts, rails and pickets, with concrete for the post holes.

Why the assumptions are on the page

Every input that affects the answer — waste percentage, bag yield, coverage per litre, coat count — is shown and editable. A calculator that hides these can only be right for one product; one that shows them is right for the product you are holding.

Nothing leaves your browser

Room dimensions and project plans are yours. The calculators run entirely on your device, nothing is sent to a server, and the pages work without a connection once loaded.