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UK calculators for DIY and the trades, with the working shown. 96 calculators across 16 trades, from paint, gravel and concrete to cable sizes, heat loss and stair rises. Enter your measurements and see how much to buy or the figure you need, with every step of the sum shown.
All 96 calculators, A to Z · Browse by trade · Project estimators
Calculators by job
Groundworks
Ballast calculator
Example: Order: 15 × cement bags and 2.31 t of ballast
Drain fall calculator
Example: Drop: 300 mm over the run (1 in 40, 2.50%)
Muck away calculator
Example: 2 × 8 yd³ skips for 6.25 m³ of loose spoil
Soakaway calculator
Example: Storage depth 1.00 m (0.74 m³ of storage for the critical storm)
Concrete and mortar
Concrete calculator
Example: Order: 114 bags
Concrete mix calculator
Example: Order: 13 × cement bags, 0.70 t sharp sand and 1.41 t gravel
Mortar calculator
Example: Order: 3 bags of cement and 0.30 t of sand
Screed calculator
Example: Order: 21 × cement bags and 2.27 t of sharp sand
Brickwork
Brick and block calculator
Example: Order: 623 units
Sand and cement calculator
Example: Order: 5 × cement bags and 0.51 t of sand (4:1 sand to cement (1:4 cement to sand))
Repointing calculator
Example: Order: 1 × bags of binder and 42 kg of sand
Wall tie calculator
Example: Order: 55 wall ties
Plastering
Coving calculator
Example: Order: 6 × 3 m lengths of coving
Plaster calculator
Example: Order: 4 × 25 kg bags of plaster (81.0 kg)
Plasterboard calculator
Example: Order: 12 boards
Render calculator
Example: Order: 8 × cement bags and 0.66 t of sand
Roofing
Roof slate calculator
Example: Order: 739 slates at a 212.5 mm gauge
Roof tile calculator
Example: Order: 641 roof tiles for 61.04 m² of roof
Flat roof calculator
Example: Membrane sheet: 3.40 × 2.40 m
Guttering and downpipe calculator
Example: Rainwater flow: 1.26 L/s from 60.0 m² of effective roof
Flooring
Flooring calculator
Example: Order: 8 packs
Self-levelling compound calculator
Example: Order: 3 bags of levelling compound (48.0 kg)
Carpet calculator
Example: Order: 18.0 m² of carpet (4 m × 4.5 m)
Loft boarding calculator
Example: You need 29 loft boards and 96 loft legs
Tiling
Tile adhesive calculator
Example: Order: 3 × bags of tile adhesive (52.8 kg)
Tile calculator
Example: You need 120 tiles
Grout calculator
Example: You need 2.82 kg of grout
Decorating
Paint calculator
Example: Buy: 1 × 5 L + 1 × 1 L
Wallpaper calculator
Example: Order: 7 rolls
Fence and decking stain calculator
Example: Order: 1 × 10 L + 1 × 5 L + 2 × 1 L (16.74 L)
Sealant and caulk calculator
Example: Order: 3 × cartridges (720 ml)
Landscaping
Gravel calculator
Example: Order: 2 bulk bags
MOT Type 1 calculator
Example: Order: 5 bulk bags
Patio calculator
Example: Order: 34 slabs, 7 × cement bags and 0.92 t of sharp sand
Sand calculator
Example: Order: 1 bulk bag
Decking and fencing
Decking calculator
Example: Order: 26 boards and 8 joists
Fence calculator
Example: Order: 6 panels and 7 posts
Postcrete calculator
Example: Order: 27 bags of post-fix (3 per post if you mix whole bags per hole: 30)
Deck substructure calculator
Example: You need 11 joists, 3 bearer lines and 9 posts
Carpentry
Skirting board calculator
Example: Order: 4 × 4.2 m lengths of skirting
Spindle spacing calculator
Example: You need 14 spindles with 95.1 mm gaps
Stair calculator
Example: Suggested: 12 risers of 216.7 mm with 241 mm goings
Stud wall calculator
Example: Order: 12 timber lengths (10 studs, 9 noggins) and 7 plasterboards
Electrics
Cable size calculator
Example: Smallest size that passes: 6 mm² (indicative)
EV charger load calculator
Example: Needs load management or a DNO check (total 77.2 A on a 60 A fuse)
Maximum demand and diversity calculator
Example: Maximum demand: about 70.6 A after diversity (indicative)
Voltage drop calculator
Example: Voltage drop: 9.00 V (3.91%)
Plumbing
Hot water cylinder size calculator
Example: Cylinder: 210 litres, about 4.1 h to heat from cold (indicative)
Water flow rate calculator
Example: Flow rate: 16.0 L/min
Expansion vessel size calculator
Example: Vessel: at least 6.77 L (indicative)
Pipe size and velocity calculator
Example: Velocity: 1.38 m/s
Heating
Boiler size calculator
Example: Boiler output: at least 29.3 kW
Heat loss calculator
Example: Heat loss: 476 W (0.48 kW) at the design temperature
Radiator size calculator
Example: Buy at least 2,996 W at ΔT50 (10,222 BTU/h)
Air conditioning size calculator
Example: Cooling: 1,344 W (4,586 BTU/h): a 5,000 BTU/h unit
Insulation and ventilation
Extractor fan size calculator
Example: Fan: at least 15 l/s (54 m³/h)
Insulation thickness calculator
Example: Insulation: at least 100.4 mm
U-value calculator
Example: U-value: 0.181 W/m²K
Condensation risk calculator
Example: Surface 9.5 °C vs dew point 12.0 °C: condensation likely
Site safety
Silica dust exposure calculator
Example: Reached the legal limit. Daily exposure 0.188 mg/m³ (8-hour TWA), 188% of the WEL
Gradient and fall calculator
Example: 1:60 = 1.67% = 0.95° = 16.7 mm per metre; drop 50 mm
Hand-arm vibration (HAV) exposure points calculator
Example: 100 points today: reached the exposure action value: action is needed to reduce exposure
Job labour time and cost estimator
Example: About 1 day on site, 2 person-days of labour
Calculators and guides by trade
Groundworks
Ballast, muck away, skips, soakaways, drain falls and m³ to tonnes: groundworks sums with the working shown and every figure editable.
Concrete and mortar
How many bags of concrete or cement and how much sand to order for slabs, footings, post holes and brickwork, with the sums shown.
Brickwork
How many bricks or blocks per square metre, how much mortar to mix and what to check before building a garden wall. UK sizes.
Plastering
How many plasterboard sheets to buy for walls and ceilings, with doors, windows and offcuts allowed for. Common UK board sizes.
Roofing
Roof tiles, slates, battens, pitch and rafter length, flat roof membranes and gutters, with BS 5534 references and pitch checks.
Flooring
How many packs of laminate, LVT or engineered wood and how much underlay and trim to buy, with layout waste and L-shaped rooms.
Tiling
How many tiles and boxes to buy, plus adhesive and grout from the figures on the bag. Straight, diagonal and herringbone layouts.
Decorating
Work out how much paint and wallpaper to buy for a room, with doors, windows, coats and pattern repeats taken into account. UK tin and roll sizes.
Landscaping
Tonnes and bulk bags of gravel, MOT Type 1, sand and topsoil for paths, patios, drives and raised beds, with typical densities shown.
Decking and fencing
How many deck boards, joists and screws, or fence panels and posts, to order for your garden, with offcuts and corners worked out.
Carpentry
Stairs to Part K, stud walls, joists, spindle spacing, skirting and architrave cut lists: carpentry sums with the working shown.
Electrics
Cable size, voltage drop, maximum demand, EV charger load and Zs to BS 7671:2018+A4:2026. Guidance for homeowners and electricians.
Plumbing
Water flow rate, pipe size and velocity, pressure from height, hot water cylinder size and expansion vessels, with the sums shown.
Heating
Room-by-room heat loss, radiator size with ΔT correction, boiler and heat pump size, underfloor heating and BTU conversions.
Insulation and ventilation
U-values against Part L, insulation thickness, loft insulation rolls, condensation risk and Part F extractor fan rates.
Site safety
Silica dust time to the WEL, hand-arm vibration points, noise exposure, scaffold bays and gradients: planning estimates, not risk assessments.
How the calculators work
Every calculator shows its formula and the typical figures it starts from, such as how many square metres a litre of paint covers or how heavy a tonne bag of gravel is. Those defaults are planning values, so you can change any of them to match the figure on your bag, pack or tin. See how we calculate.