Building & DIY Calculators

Free building calculators for UK DIY and home projects. Work out how many decking boards, tiles or bulk bags of topsoil you need, find the pitch of a roof, size a staircase to building regulations or get an indicative steel beam size. Everything is in metric, using standard UK product sizes.

  • Building calculators16
  • UnitsMetric (m, mm, m², m³)
  • CheckedNovember 2026

Building and materials calculators

Square metre calculatorWork out area in m² from metres, cm, feet or inches.Decking calculatorDeck boards, joists, screws and cost for your deck size.Pond volume calculatorLitres and gallons in your pond, plus liner and pump size.Roof pitch calculatorFind the pitch of a roof in degrees, ratio and per cent.Steel beam calculatorIndicative UB size, weight and cost for a domestic steel beam.Topsoil calculatorHow much topsoil you need in m³, tonnes and bulk bags.Stair calculatorRisers, goings, pitch and Part K checks for a staircase.Tile calculatorHow many tiles, boxes, adhesive and grout you need.Downlight spacingHow many downlights a room needs and how far apart.Spindle spacingSpindle count and gaps that pass the 100 mm sphere rule.Roof area calculatorRoof area from footprint and pitch, plus tiles needed.Brick calculatorBricks, mortar, sand and cement bags for a wall.TV mount heightBest height and viewing distance for a wall-mounted TV.U-value calculatorU-value of a wall, roof or floor build-up vs Part L.Grout calculatorHow much grout you need in kg for your tiles and joints.Block calculatorConcrete blocks, mortar, sand and cement for a wall.

What each calculator does

CalculatorWhat it works out
Square metre calculatorWork out area in m² from metres, cm, feet or inches.
Decking calculatorDeck boards, joists, screws and cost for your deck size.
Pond volume calculatorLitres and gallons in your pond, plus liner and pump size.
Roof pitch calculatorFind the pitch of a roof in degrees, ratio and per cent.
Steel beam calculatorIndicative UB size, weight and cost for a domestic steel beam.
Topsoil calculatorHow much topsoil you need in m³, tonnes and bulk bags.
Stair calculatorRisers, goings, pitch and Part K checks for a staircase.
Tile calculatorHow many tiles, boxes, adhesive and grout you need.
Downlight spacingHow many downlights a room needs and how far apart.
Spindle spacingSpindle count and gaps that pass the 100 mm sphere rule.
Roof area calculatorRoof area from footprint and pitch, plus tiles needed.
Brick calculatorBricks, mortar, sand and cement bags for a wall.
TV mount heightBest height and viewing distance for a wall-mounted TV.
U-value calculatorU-value of a wall, roof or floor build-up vs Part L.
Grout calculatorHow much grout you need in kg for your tiles and joints.
Block calculatorConcrete blocks, mortar, sand and cement for a wall.

Measuring up for a DIY project

  • Measure in metres and millimetres, and write every measurement down before you start.
  • Work out the area first with the square metre calculator, splitting awkward shapes into rectangles.
  • Add a waste allowance: about 10% for most materials and 15% for diagonal layouts.
  • Buy tiles, boards and paint from the same batch so colours match.
  • Check whether your project needs planning permission or building regulations approval before you order.

Price the job

Once you know the quantities, use our home improvement cost calculators to price decking, patios, fencing, flooring, extensions and more at 2026 UK prices.

Frequently asked questions

Are these building calculators accurate?

They use standard formulas and typical UK product sizes, so the quantities are reliable for planning and ordering. Always add a waste allowance and check product data sheets before you buy.

Do the calculators use metric or imperial units?

All building calculators work in metric (metres, millimetres, m² and m³), which is what UK builders’ merchants use. The square metre calculator also converts to and from square feet.

Can I use the steel beam calculator for building control?

No. It gives an indicative size for budgeting only. Building control needs structural calculations from a qualified engineer.

Which UK regulations do the calculators follow?

The stair calculator checks Approved Document K for private stairs in England. Planning notes refer to permitted development rules in England; Wales, Scotland and Northern Ireland can differ.

How much extra material should I order?

Usually 10% for tiles, decking and paving (15% for diagonal or herringbone layouts) and around 10% extra topsoil to allow for settling.