Construction & DIY Calculators
Work out how much material a job actually needs — concrete, paint, tiles or flooring — before you order, with waste allowance built in.
Estimating material is a volume or an area problem
Almost every DIY quantity question reduces to one of two shapes. Concrete is a volume: length × width × depth, which the Concrete Calculator converts into cubic metres, bag counts and weight. Paint, tiles and flooring are areas: the Paint Calculator divides your wall area by the coverage rate on the tin and multiplies by the number of coats, while the Tile Calculator and Flooring Calculator divide floor or wall area by the size of a tile or pack.
Always order more than the maths says
Every one of these calculators includes a waste allowance, and it is not padding. Tiles break, boards are cut to fit at the edges, and paint is absorbed unevenly by fresh plaster. Ten per cent is the normal allowance for a simple rectangular room, and fifteen per cent for diagonal tile layouts, herringbone flooring or rooms with lots of cuts around fittings. Running out mid-job means a second delivery, a batch that does not quite match, and a wasted day.
Measure the space, not the plan
Rooms are rarely square and drawings are rarely current. Measure each wall at floor level and again at head height, and use the larger figure. Deduct large openings — doors, windows, a fireplace — but do not deduct small ones; the offcuts are rarely reusable. If your measurements are in feet and inches and the product is sold in metric, convert first with the Area Converter or the Length Converter rather than rounding as you go.
What these tools do not cover
These are quantity estimators, not structural or specification tools. They will not tell you what concrete mix to use, whether a floor can carry the load, what primer a surface needs, or how a substrate should be prepared. Follow the manufacturer's data sheet for coverage rates and curing times, and consult a qualified professional for anything structural. The coverage rates, waste allowances and conversion factors these tools apply are listed on our construction & DIY reference page.