Project guides
How much do I need? DIY materials guides
Plain-English answers to the questions people ask before a trip to the merchant. Each guide gives you the formula, a worked example, a calculator and a full checklist, based on manufacturer guidance.
Indoor jobs
How much paint do I need for a room?To work out how much paint you need for a room, measure the walls, take off doors and windows, multiply by the number of coats and divide by 12. Here is the rule, a worked example and a calculator that does it for you.
How many plasterboards do I need?To work out how many plasterboard sheets you need: each standard 2400 x 1200mm sheet covers 2.88 m². Divide your area by that, add 10% for cuts, then work out the screws, tape and plaster to go with it.
How much plaster do I need to skim a wall or room?A finish skim is about 2mm thick. British Gypsum says a 25kg bag of Multi-Finish covers about 10 m² at that thickness.
Stud wall materials list: what do I need?A timber stud partition is CLS studs at 400mm centres between a head and sole plate, boarded both sides. Here is the full stud wall materials list, including how much timber, and how much of each.
How many tiles do I need, and how much adhesive and grout?To work out how many tiles you need, find the area, divide by the size of one tile and add 10% for cuts. Adhesive and grout depend on where you are tiling and the joint size.
Tiling a floor: how many tiles, and how much adhesive and grout?Measure the floor, add an allowance for cuts, then work out adhesive and grout from the tile size.
Tiling a wall or splashback: tiles, adhesive and groutMeasure the wall, take off anything you are not tiling, add an allowance for cuts and work out adhesive and grout from the tile size.
Fitting an internal door: what do I need to buy?Hanging a door is more than the door. This list covers the door, hinges, handle and latch, the lining, the gap filler and the architrave, and how many of each you need for more than one door.
How much skirting board do I need?Skirting runs round every wall except the doorways. Measure the walls, take off the doors, add an allowance for the cuts and divide by the length you are buying.
How much laminate flooring do I need?Measure the room length and width to get the area in m², add 10% for cuts, then add underlay, beading for the expansion gap and a door bar for each doorway.
How many rolls of wallpaper do I need?To work out how many rolls of wallpaper you need, count the drops across the walls, work out how long each drop is once the pattern repeat is allowed for, and see how many drops each 10.05m roll gives.
How much loft insulation do I need for 270mm?The Energy Saving Trust recommends 270mm of mineral wool in a loft. Here is how many rolls of loft insulation that takes, from scratch or as a top-up.
How much paint do I need for new plaster?Fresh plaster is thirsty. It needs a thinned mist coat to seal it before the full coats, so you need more paint than for a repaint. Here is how much, and how to do it.
How much plasterboard do I need for a ceiling?Replacing an old lath and plaster or cracked ceiling starts with the area. Multiply the length by the width, divide by the sheet size and add a little for cuts, then work out the screws and the skim.
How many floor tiles do I need for a bathroom?Bathroom floors are small but full of cuts: round the toilet, the basin pedestal and the bath panel. Measure the floor, add the waste allowance and buy whole boxes from one batch.
Planning and budgets
Garden and outdoor jobs
How many fence panels and posts do I need?Divide the length of the run by the panel width and round up. You need one more post than panels, plus one for each corner or gate.
How many feather-edge boards for a closeboard fence?A closeboard fence is built on site from posts, arris rails and overlapping feather-edge boards. The overlap decides how many feather-edge boards per metre you need, and it is what most lists get wrong.
How much decking do I need?Boards are the easy part. The frame underneath is where most DIY lists go wrong, so this guide follows the Timber Decking & Cladding Association (TDCA) handbook.
How much concrete for a shed base?Make the base a little bigger than the shed, work out the volume, and convert it to bags of cement and ballast for a 1:5 mix.
How much sand and cement do I need for bricks, blocks or slabs?Work out the volume of mortar first, then split it into cement and sand by the mix. Here are the standard UK rates for brickwork, blockwork and laying paving slabs.
How many paving slabs do I need, and how much sub-base?To work out how many paving slabs you need, divide the patio area by the area of one slab and add 10% for cuts. The sub-base, mortar bed and jointing follow from the same area.
How much gravel do I need? Tonnes and bagsTo work out how much gravel you need, multiply the area by the depth to get cubic metres, then by the weight of a cubic metre of your gravel to get tonnes.
How much artificial grass do I need, and what goes under it?To work out how much artificial grass you need, decide which way the rolls will run, count the strips of 2m or 4m wide grass, and add a little length for trimming. The base underneath matters as much as the grass.
How many sleepers for a raised bed, and how much soil?A sleeper raised bed is a simple box, but the corners, the screws and the soil volume are where lists go wrong. This guide follows the BSW sleeper installation guidance.
How we work out quantities
Every guide uses the same formulas as the SmartBuild app, with coverage figures from manufacturers' data sheets (British Gypsum, Knauf, Dulux, Heidelberg Materials, Marshalls and others) and the Timber Decking & Cladding Association. Each page lists its sources. We add a sensible allowance for cuts and waste and round up to whole packs, and we never write prices into the guides: the app prices your list from live supplier feeds.
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