Block calculator

How many concrete blocks for a wall, with the mortar, bags of cement and sand. Choose 100, 140 or 215 mm blocks, and take off the openings.

Put these calculators on your phone, free

They work like an app from your home screen, even with no signal on site. On an iPhone: tap Share, then Add to Home Screen. On Android: tap the menu (⋮), then Add to Home screen or Install app.

The free SiteHelm phone app for iPhone and Android is on its way, with every calculator in it. Tell me when it's out

Do more with SiteHelm PRO

Take the wall lengths off the drawing with Take-off and the blocks, mortar and ties go into an order or a quote. Save the figures to the job.

Free on your phone. Every builders' calculator will be free in the SiteHelm phone app for iPhone and Android, coming soon. Tell me when it's out.

Every builders' calculator is in SiteHelm PRO for your Windows PC, alongside take-off, RAMS, quotes, invoices and 40+ more tools. The first 100 get a free 1-year licence.

Get a free 1-year licence See the prices

Worked example

The inner leaf of an extension wall 10 m long and 2.4 m high in 100 mm blocks, with 3.6 m² of windows and doors, in a 1:5 mortar:

212 blocks to order

20.40 m² of wall
9.88 blocks per m² of one skin (201 before waste)
0.15 m³ of mortar
2 bags of cement (25 kg) and 0.26 tonnes of building sand at 1:5

How the sum works

A standard block face is 440 × 215 mm. With a 10 mm joint each block takes up 450 × 225 mm, so a square metre takes 1,000,000 ÷ (450 × 225) = 9.88 blocks. Most people call it 10 per m².

The thickness (100, 140 or 215 mm) doesn't change the count per m², but it changes the mortar: a thicker block has a deeper joint to fill.

Mortar, cement and sand

The mortar is the joints' volume plus 10 percent, with 1.33 m³ of dry mix for each m³ of mortar, split by the mix. Cement is counted in 25 kg bags and sand in tonnes. Use the mix the specification or the engineer gives you.

Before you order

Block weights differ a lot between dense, medium and lightweight blocks, so check the handling on the supplier's sheet: HSE advises against blocks over 20 kg being laid by hand repeatedly. For a cavity wall, work out each leaf with its own block and add the ties once.

Guides that go with it

How many bricks and blocks per square metre?A standard UK brick wall takes about 60 bricks per m2 (half-brick) or 120 (one-brick), and blocks about 10 per m2. The sum, waste and openings explained.How do I do a quantity take-off from drawings?How to take off quantities from drawings for a small job: scale check, set order, deductions, waste and pricing, with a worked garden room example.What do the Manual Handling Regulations require on a building site?Manual Handling Regulations for builders: avoid, assess, reduce, the TILE factors, and practical controls for blocks, kerbs, plasterboard and cement.

More builders' calculators

Brick calculatorHow many bricks for a wall, with mortar, bags of cement and tonnes of sand. single or double skin, openings and waste.Concrete calculatorM3 to order as ready-mix, or the bags of cement and tonnes of sand and gravel to mix it.Type 1, gravel and sand calculatorTonnes of mot type 1, gravel, sharp sand, ballast, scalpings or topsoil for an area and depth, with bulk bags and loads.Excavation and muck-away calculatorThe volume dug from a trench or a reduced dig, bulked up by soil type, with the tonnes, skips and grab lorry loads to take it away.Volume calculatorTanks, pits, piles, ramps and soakaways.Roof pitch and rafter calculatorPitch from the rise (or rise from the pitch), rafter length with the overhang, the stock length to buy, rafters per side and roof area.Stair calculatorNumber of risers, rise and going, pitch and the 2r + g rule, checked against approved document k for a house, utility or general stair.U-value calculatorBuild up a wall, roof or floor layer by layer and check it against part l for an extension or new home, with the insulation needed to pass.Roof slate and batten calculatorBatten gauge, slates per m², slates to order, metres of batten and nails, from the roof area, slate size and headlap.Plaster calculatorBags of finish plaster for a skim, or hardwall or bonding and finish for float and set, from the wall and ceiling area.Tile calculatorHow many tiles and boxes for a wall or floor, with adhesive and grout, for any tile size, joint and laying pattern.Screed calculatorM3 of screed for a floor, the bags of cement and tonnes of sharp sand for a 1:4 sand and cement screed, or liquid screed to order.

Every calculator

The construction manager’s toolbox.

Measure from a drawing, Easy CAD, Edit PDF and Weather are free for good in your browser. Take-off, RAMS, quotes, invoices and 40+ more tools come with SiteHelm PRO.

Open SiteHelm Free See the founding offer