Construction Calculators

Get the dew point from temperature and humidity, then check any wall, roof or floor for surface condensation and mould risk. BS EN ISO 13788.

Build your wall, roof or floor layer by layer to get the U-value in W/m²K, with an Approved Document L compliance check. Metric, BS EN ISO 6946 method.

Work out how much loft insulation you need to reach 270 mm, how many rolls or bags to buy, material cost and the indicative U-value band.

Work out how many rolls of wallpaper you need using the drop-counting method, with pattern repeat, match type and wastage. Metric, standard 10.05m × 0.53m rolls.

Free UK paint coverage calculator. Work out how many litres of paint you need for walls and ceilings with real-world coverage rates, tin recommendations and mist coat for new plaster.

Calculate how many bags of concrete you need for a slab based on size, thickness, and bag weight.

Calculate dry pour concrete volume and bags needed for a slab with metric and imperial support.

Calculate concrete volume and bags needed for a 2-inch thick slab with metric and imperial support.

Calculate the weight of a concrete slab in kg, tonnes and lb from length, width and thickness.

Calculate concrete volume for a monolithic slab (slab-on-grade) including thickened edges.

Estimate concrete volume for trench footings, pad footings, and round post holes — plus bags and cost.

Calculate concrete volume for slabs, footings, and columns with metric and imperial support and bag estimator.

Calculate rebar weight per metre, total weight, and tonnes with diameter and length.

Convert concrete volume into estimated ready-mix truck loads. Choose truck sizes, add wastage, and see loads plus remainder.

Free UK mortar calculator. Work out sand, cement and mortar for brickwork and blockwork by wall area or brick count, with mix ratios and wastage.

Work out sand, cement and liquid screed for any floor area and depth, with mix ratios, wastage and material costs.

Convert rise and run into pitch ratio, degrees, and slope instantly with metric and imperial support.

Work out gauge, tiles per m² and total tiles for plain, interlocking, pantile and slate roofs.

Calculate correct roof batten spacing based on tile gauge, roof pitch and tile type.

Calculate rafter length using pitch, roof span/run, overhang, and optional birdsmouth allowance. Metric-first.

Work out how many bricks you need for a wall, with mortar joints and waste included.

Calculate how many tiles you need for floors, walls, showers or bathrooms. Supports m², sq ft, cm & mm.

Calculate deck stair steps, rise/run and stringer length for 2×10 or 2×12. Metric & imperial.

Work out how many studs, plates, noggins and plasterboard sheets you need for a timber partition wall. Metric, UK CLS sizes, 400mm or 600mm centres.

Find the maximum clear span for C16 or C24 floor joists at 400–600 mm centres, or the joist size you need for a given span.

Work out the number of steps, individual rise, going and pitch for a domestic staircase to Approved Document K, with pass/fail compliance checks and stringer length.

Work out how many stock lengths to buy, total volume in m³, offcut waste and estimated cost for any timber section. Supports all common UK carcassing and CLS sizes.

Quickly calculate the area of your decking project in square metres or square feet, including waste allowance for both rectangular and circular decks.

Free UK plasterboard calculator. Work out how many sheets you need for walls, ceilings or a whole room, in metric, with a waste allowance and standard UK board sizes.

Fast voltage drop calculator for DC, single-phase AC, and three-phase AC. Supports copper/aluminium, metric mm² and AWG/kcmil, power loss, and auto cable sizing.

Free UK cable sizing calculator to BS 7671. Enter load, length, install method and ambient temperature to get the recommended copper cable size with a voltage drop check.

Estimate the cost of a single-storey, double-storey or wrap-around house extension with 2026 UK regional rates, cost per m², kitchen, glazing, underfloor heating and professional fees.

Work out CIS deductions at 20% or 30% on the labour element of a subcontractor invoice, with materials excluded. Free UK calculator with 2026/27 rates.

Estimate the cost of a dormer, hip-to-gable, mansard or rooflight loft conversion by floor area, region and finish, with 2026 UK build rates and professional fees.

Estimate the cost of a new roof or full re-roof — concrete tiles, clay, natural slate or a flat roof — with scaffolding, waste, region and complexity factored in. 2026 UK rates.

Estimate the cost of a new patio — sandstone, porcelain, block paving, limestone, granite or concrete slabs — with 2026 supply-and-fit rates, groundwork, waste, edging, region and VAT.

Work out how much topsoil you need in cubic metres, litres, tonnes and bulk bags from your area and depth, with a wastage allowance.