Home & DIY
Shopping lists for DIY jobs: concrete, decking, stud walls, skirting and radiator sizes, worked out in your browser with UK sizes. Learn more
Concrete Calculator
Bags, cement and ballast or ready-mix for slabs, paths and post holes.
Decking Calculator
Boards, joists and screws for a deck, with offcuts reused.
Radiator Size (BTU) Calculator
Room heat loss and the radiator size for a boiler or heat pump.
Skirting, Coving & Architrave Calculator
Lengths of skirting, coving or architrave to buy, with a cutting plan.
Stud Wall Calculator
Timber, plasterboard and screws for a stud partition with doors.
Free DIY calculators that tell you exactly what to buy
Buying too little means a second trip to the builders’ merchant halfway through a job; buying too much leaves bags of cement going hard in the shed. These calculators work out real shopping lists, not just areas. The Concrete Calculator covers slabs, paths, footings and fence-post holes, and gives the answer three ways: ready-to-use bags, cement and ballast to mix yourself at 1:4, 1:5 or 1:6, or a ready-mix delivery. The Decking Calculator counts boards, joists and screws, and plans the cuts so offcuts from one row finish another.
Indoors, the Stud Wall Calculator lists every stud, plate, noggin and door head for a timber partition, plans them out of standard CLS lengths, and adds the plasterboard sheets and screws to cover it. The Skirting, Coving & Architrave Calculator handles awkward rooms with chimney breasts and bays, takes doorways out of the skirting, and works out architrave legs and heads for standard UK doors.
For heating, the Radiator Size (BTU) Calculator goes beyond the usual rule of thumb: it adds up the heat lost through the walls, windows, floor, ceiling and draughts, then converts the result to the ΔT50 rating printed in radiator catalogues, corrected for the cooler water of a condensing boiler or heat pump. Everything works in metric with UK sizes, runs in your browser, and remembers your last figures on your device.
Questions and answers
- Should I buy bags of concrete, mix my own or order ready-mix?
- Ready-to-use bags are easiest for a few post holes or a small pad, but they add up quickly: a cubic metre takes over 100 of them. Mixing your own from cement and all-in ballast is far cheaper for a shed base or path. Above about half a cubic metre, a ready-mix or mix-on-site delivery is usually cheapest of all and saves hours of mixing. The Concrete Calculator shows all three for your job so you can compare.
- Why does the radiator calculator give a bigger number for a heat pump?
- The heat a room needs is the same, but a radiator gives out less when the water in it is cooler. Catalogues quote output at ΔT50, with water on average 50 °C hotter than the room. A condensing boiler running at 70/50 °C gives about ΔT40, so a radiator produces around three-quarters of its rated output; a heat pump at 45/40 °C gives about ΔT21, or roughly a third. So you need a bigger catalogue figure to deliver the same heat.
- Should stud walls be at 400 mm or 600 mm centres?
- Both divide evenly into a 1200 mm sheet of plasterboard, so the board edges always land on a stud. 600 mm is standard for 12.5 mm board and saves timber; 400 mm makes a firmer wall and is needed for 9.5 mm board, for tiles, and wherever you plan to hang heavy things. The Stud Wall Calculator shows how the timber count changes.
- How many lengths of skirting should I buy, compared with just dividing the perimeter?
- Dividing the room’s perimeter by the length of a board undercounts, because each wall is cut separately and a short offcut can’t always be used anywhere else. The Skirting, Coving & Architrave Calculator plans each wall from whole lengths, reuses offcuts where they fit, and only joins boards on walls longer than one length. That usually means one or two more lengths than the simple sum, plus a spare for a mitre cut the wrong way.
- Do decking boards need to join over a joist?
- Yes. Both board ends need something solid to screw into, so make every join over a joist, ideally doubled or with a noggin alongside, and stagger the joins between neighbouring rows so they don’t line up. The Decking Calculator warns when your deck is longer than the boards and counts the joins, and also tells you if the last row needs ripping down to fit.