How to Estimate Concrete Works

Formwork is estimated as its own line item, separate from the concrete itself, because it carries a different labour and material cost — timber or steel formwork, bracing, and the labour to erect and strip it. It is typically measured in m2 of contact area, meaning the vertical face of formwork touching the wet concrete, or as a lineal metre rate for simple straight edge-forms where the depth stays constant.

A straight slab edge with a consistent depth is usually priced per lineal metre, while footings, columns and beam soffits and sides are priced per m2 of contact area because the formed face varies in height or shape.

• Slab edge formwork: usually priced per lineal metre where the edge depth is constant along its run.
• Footing formwork: m2 of contact area on the vertical faces, doubled where both sides of a trench are formed above ground level.
• Column and beam formwork (sides and soffits): m2 of contact area, often at a higher rate to reflect bracing and stripping labour.
• Complex formwork — curves, steps, penetrations or voids: priced at a higher m2 rate to reflect the extra cutting and fitting time.

Reinforcement is estimated as two separate systems, because mesh and bar are bought and measured differently. Mesh is priced per m2, with an allowance added for the standard overlap, or lap, between adjoining sheets. Bar reinforcement and ligatures are priced by weight — kilograms on smaller jobs, tonnes on larger ones — because bar is supplied and fixed by mass, not area.

Converting a bar schedule into a weight relies on standard mass-per-metre tables for each bar diameter, so the takeoff needs both a length and the correct bar size to price accurately.

• Mesh (for example SL72 or SL82): measured by m2 of slab area, plus a lap allowance where adjoining sheets overlap.
• Reinforcing bar: measured as a length per bar type and diameter, then converted to kg or tonnes using standard mass-per-metre figures.
• Ligatures and stirrups: counted individually against the cage or column spacing, then converted to a mass for pricing.
• Bar chairs, spacers and tie wire: a small but real cost, usually allowed for as a percentage of the reinforcement supply cost rather than measured item by item.

Placing concrete is labour-intensive with several distinct stages, and each is commonly priced as its own component rather than folded into a single generic pour rate: placing (getting concrete from the truck or pump line into the formwork), vibrating (removing entrapped air), screeding (levelling to finished level and fall), finishing (steel trowel, broom, or an exposed or coloured finish), and curing (protecting the pour while it gains strength).

Pump or boom hire is priced as its own plant line — typically a call-out or hourly rate plus a rate per m3 pumped — because it is a hired cost rather than a labour cost.

• Place: labour to pour and spread concrete into the formwork, whether from a truck chute, barrow run or pump line.
• Vibrate: poker or screed vibration to remove air and consolidate the pour around reinforcement.
• Screed: levelling the pour to the correct finished level and fall.
• Finish: steel trowel, broom, or an exposed aggregate or coloured finish — the finish type materially changes the labour rate.
• Cure: curing compound, plastic sheeting or wet hessian, priced to protect early strength gain.

Concrete estimates always allow for wastage above the calculated m3, because the volume actually ordered is higher than the theoretical area-times-thickness figure. Subgrade variation, formwork give under load, and ordinary spillage during the pour all add to the volume delivered versus the volume calculated from plan dimensions.

Reinforcement carries a separate wastage allowance of its own, for bar cut-offs and lap overlaps, distinct from the concrete wastage allowance.

• Slab and footing pours commonly carry a wastage allowance over the calculated volume to cover subgrade variation and formwork give.
• Reinforcement carries its own separate allowance for cut-offs and lap overlaps, on top of the mesh lap already built into the area measurement.
• Concrete is often supplied in whole truck-load increments, so the ordered volume is commonly rounded up rather than exact.
• Under-ordering risks a costly second truck call-out; over-ordering wastes paid-for material — so an accurate takeoff matters more than the wastage percentage itself.

A small error in measured slab thickness or reinforcement quantity does not stay small — it compounds across every part of the build-up at once, because supply, pump volume and labour are all priced against the same measured figure. Understate a 150mm slab as 125mm and the shortfall shows up simultaneously in concrete supply, pump volume charged, and the labour to place and finish the extra depth once it is corrected on site.

Reinforcement errors compound in a similar way. Missing a lap allowance or under-counting bar length affects supply cost directly, and can also mean a structural non-conformance that has to be fixed after the pour — a far more expensive correction than getting the quantity right at takeoff.

Putting the elements above together, a concrete estimate reads as a single build-up per pour: supply volume, formwork, reinforcement and labour, each priced against your own rates and added together for a total. The figures below are illustrative only, based on a 100m2 slab at 150mm thick, and are not MTH pricing — every business applies its own rates for each line.