Pick one system per calculation
If you measure the room in feet, keep paint coverage in square feet per gallon. If you measure in metres, use litres and square metres. Do not convert halfway through in your head.
Project Home Calc tools expose unit toggles so the formula stays the same while labels change.
Volume materials
Concrete and gravel are cubic yards or cubic metres; weight is tonnes or tons depending on the market. Supplier tickets may use one while your drawing uses the other — convert once on paper, then stick to it.
Paint and coverage
US cans talk in gallons and square feet; UK tins in litres and square metres. Coverage claims assume ideal surfaces — real walls usually need more product than the optimistic number.
Money lines
The Cost Estimator uses the currency mindset you enter as a unit price. A US price per gallon and a UK price per litre are not interchangeable without converting both price and volume.
When comparing online guides, check whether prices are materials-only or installed. Mixing those categories is a common reason DIY budgets look impossibly cheap next to contractor quotes.
If a supplier lists both metric and imperial pack sizes, pick one system for the whole order sheet and stick to it until delivery day.
Use a calculator for this
Concrete Calculator
Work out how much ready-mix concrete a slab, footing, or column needs.
CalculatePaintingPaint Calculator
Estimate how much paint a room needs, based on wall area and coats.
CalculateConstructionGravel Calculator
Estimate gravel volume and weight for a driveway, path, or sub-base.
CalculateCost EstimationProject Cost Estimator
Roll materials, labor, delivery, waste, and optional markup into a planning total.
CalculateFrequently asked questions
Does the site auto-detect my country?
Tools let you choose units explicitly so a VPN or travel location cannot silently change your maths.
Are formulas different for the UK?
The geometry is the same. Product pack sizes and labelling differ — always match the calculator output to the product you will buy locally.
Should I convert every measurement twice to be safe?
No — convert once into the system you will buy in, write it down, and run the calculator in that system. Repeated conversions introduce rounding errors.