Should I order ready-mixed concrete or buy bags?

That depends on the volume, on access to the site and on local prices. The concrete calculator shows both the volume to order and the number of bags, so you can compare. Ask the supplier about the smallest delivery and about charges for part loads.

Why is the weight of gravel or soil only approximate?

The weight of loose material depends on the kind of stone or soil, on the size of the pieces and on how wet it is. The calculator uses a bulk density that you can change. Ask your supplier for the value of the material you are buying.

How much extra flooring should I buy?

The flooring calculator starts with 10 percent, which you can change. One manufacturer, Quick-Step, advises 5 percent for a regular room and 10 percent for a room with many angles and curves. Follow the recommendation of the manufacturer of your floor where there is one.

Does the decking calculator design the structure of my deck?

No. It counts boards and joists for the spacing you enter. The size of joists, beams, posts and footings and the connection to the house are structural questions that depend on your building code.

Floor and outdoor calculators

Nine calculators for floors, decks, patios, garden walls and other outdoor projects. They turn sizes into boxes, boards, pavers, blocks, bags, cubic metres or cubic yards.

Last updated: September 29, 2026

In this section

FlooringCalculate how many boxes of laminate, vinyl plank, engineered wood or carpet tile to buy from the room size, the coverage of one box and an allowance for cuts.
DeckingCalculate how many deck boards and joists a rectangular deck needs from its size, the board width and length, the gap between boards and the joist spacing.
ConcreteConcrete for a slab, strip footing, Sonotube column or steps in cubic yards or m³, and bags of 40 to 80 lb or 20, 25 or 30 kg if you mix it yourself.
Fence post concreteHow many bags of concrete per fence post: round or square holes, 4×4 or 100 mm posts, a gravel base, and bag sizes for the US, Canada, UK, Australia and NZ.
GravelHow much gravel for a driveway, path or French drain: cubic yards or m³, tons or tonnes and truckloads, with stone presets based on supplier weights.
MulchHow many bags or cubic yards of mulch for a rectangular or round bed or a ring around a tree, with 1.5, 2 and 3 cu ft bags or 50 to 100 L bags.
TopsoilHow much topsoil or raised bed soil to buy: cubic yards or m³, bags and approximate weight for a lawn or garden area or for several raised beds.
Paver patioHow many pavers for a patio, with joint width, a pattern allowance, the base gravel and bedding sand in cubic yards and tons, edging, and round fire-pit patios.
Retaining wallHow many retaining wall or garden wall blocks, caps and tons of base and drainage gravel you need, including round fire pits, with the height limits to know.

Area, depth and volume

Flooring and decking are bought by area. Concrete, gravel, mulch and topsoil are bought by volume, which is the area multiplied by the depth of the layer.

The most common mistake is to mix units: an area in metres with a depth in millimetres, or an area in feet with a depth in inches. The calculators ask for each value in the unit that people normally measure it in and convert it for you.

Which calculator to use

Flooring: boxes of laminate, vinyl plank, engineered wood or carpet tile for a floor area.
Decking: deck boards by length and the number of joists under them.
Concrete: volume for slabs, strip footings and round post holes, and the number of bags if you mix it yourself.
Fence post concrete: bags per post and for a whole fence, with the post and a gravel base subtracted.
Gravel: cubic yards or m³, tons or tonnes and truckloads for an area or a French drain.
Mulch: bags and cubic yards for rectangular and round beds and rings around trees.
Topsoil: cubic yards, bags and weight for an area or for raised beds.
Paver patio: pavers, base gravel and bedding sand in cubic yards and tons, and edging, for square, round and fire-pit patios.
Retaining wall: blocks, caps and gravel for garden and retaining walls and round fire pits, with the height limits to check.

Frequently asked questions

Should I order ready-mixed concrete or buy bags?: That depends on the volume, on access to the site and on local prices. The concrete calculator shows both the volume to order and the number of bags, so you can compare. Ask the supplier about the smallest delivery and about charges for part loads.
Why is the weight of gravel or soil only approximate?: The weight of loose material depends on the kind of stone or soil, on the size of the pieces and on how wet it is. The calculator uses a bulk density that you can change. Ask your supplier for the value of the material you are buying.
How much extra flooring should I buy?: The flooring calculator starts with 10 percent, which you can change. One manufacturer, Quick-Step, advises 5 percent for a regular room and 10 percent for a room with many angles and curves. Follow the recommendation of the manufacturer of your floor where there is one.
Does the decking calculator design the structure of my deck?: No. It counts boards and joists for the spacing you enter. The size of joists, beams, posts and footings and the connection to the house are structural questions that depend on your building code.