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Home improvement calculators
Measure once, buy the right amount: calculators for concrete, gravel, mulch, paint, decking and roofs, in feet and inches or metres.
Home improvement calculators
- Square footage calculatorAdd up the square footage of rectangles, L-shapes, circles and triangles in feet, inches or metres, with square metres, acres and cost per square foot.
- Concrete calculatorWork out concrete for slabs, footings, columns and steps in cubic yards or cubic metres, and how many 40, 60 or 80 lb or 20 or 25 kg bags to buy.
- Gravel calculatorWork out gravel volume and weight in metric tonnes or US short tons for one or more areas, with cost.
- Mulch calculatorCalculate mulch for your beds in cubic metres, feet and yards, whole bags, and bag versus bulk cost.
- Paint calculatorWork out paint for walls and ceilings minus doors and windows, coats and coverage, and which tins to buy.
- Deck calculatorCount decking boards for your deck size, board direction and stock length, with offcuts, cost and a layout preview.
- Roof pitch calculatorConvert rise and run, angle or X:12 pitch, and work out rafter length with a labelled diagram.
Which calculator do you need?
- Measuring a room, floor or plot? Start with the Square Footage Calculator. It adds up rectangles, L-shapes, circles and triangles and gives square feet, square metres and acres.
- Pouring a slab, footing, post holes or steps? The Concrete Calculator gives cubic yards or cubic metres and the number of 40, 60 or 80 lb (or 20, 25 or 30 kg) bags.
- Laying a driveway base or path? The Gravel Calculator converts area and depth into volume and weight in tonnes or US tons.
- Topping up garden beds? The Mulch Calculator gives bags and cubic yards and compares bagged with bulk prices.
- Painting walls or ceilings? The Paint Calculator takes off doors and windows, multiplies by coats and suggests which cans or tins to buy.
- Building a deck? The Deck Material Calculator counts boards for your board length and direction, including offcuts.
- Working on a roof? The Roof Pitch Calculator converts between X:12 pitch, angle and rise over run and works out rafter length.
Measure first, then add a margin
Nearly every materials estimate is area times depth (or thickness), converted into the unit the supplier sells in. Most mistakes come from mixing units: a 4-inch slab is 1/3 ft thick, not 4 ft. These calculators take each measurement in the unit you'd naturally use and do the conversion for you.
Real jobs use more than the plan. Ground is uneven, forms bow, boards split and some paint stays in the tray. Add an allowance: 5–10% is common for concrete, and more for hand-dug holes or a rough sub-base. Where a calculator rounds up to whole bags, boards or cans, it shows the exact figure too, so you can see how much is spare. For a step-by-step concrete example with real numbers, read how much concrete do I need?
Why use these calculators
- Imperial and metric. Enter feet and inches or metres and centimetres.
- Private and free. Every calculation runs in your browser. There's no account and nothing you enter is sent anywhere.
- Clear about assumptions. Bag yields, coverage rates and densities are shown so you can match them to the product you're buying. The label on the bag or can always comes first.
Guides
Frequently asked questions
How many bags of concrete are in a cubic yard?+
A cubic yard is 27 cubic feet. An 80 lb bag of QUIKRETE Concrete Mix yields about 0.60 cubic feet, so a yard takes 45 bags; at 0.45 cubic feet per 60 lb bag it takes 60. Add your waste allowance and check the yield on the bag you buy. The Concrete Calculator does this for you.
Should I buy bagged concrete or order ready-mix?+
Bags suit small jobs such as post holes, pads and steps. Once you need more than about a cubic yard, mixing that many bags by hand is slow and hard to keep consistent, so ready-mix is usually easier. Check your local supplier's minimum order and short-load fee first.
How do I calculate the square footage of an L-shaped room?+
Split it into two rectangles, multiply length by width for each, and add the two results. The Square Footage Calculator lets you add several shapes and totals them.
How much extra material should I order?+
A 5–10% allowance is typical for concrete, gravel and mulch. Decking needs extra for offcuts and boards you reject, and paint depends on the surface; rough or porous walls take more. Order a little extra rather than run short partway through a pour or a coat.
How deep should mulch or gravel be?+
A layer of 2–3 inches (5–7.5 cm) of mulch is the usual advice for garden beds. Gravel depth depends on use: paths need less than a driveway, which also needs a compacted base layer. Enter your own depth in the Mulch or Gravel Calculator.
What does a 6:12 roof pitch mean?+
The roof rises 6 inches for every 12 inches it runs horizontally, an angle of about 26.6 degrees. The Roof Pitch Calculator converts between pitch, angle and rise over run.
Are these calculators accurate enough to order from?+
The arithmetic is exact. Accuracy depends on your measurements and on the coverage or yield of the product you choose, so measure carefully, use the manufacturer's figures and add a margin. For structural work, follow your plans and local building code.