How do I calculate beam concrete volume?

Multiply span by width by depth for one beam, then by the number of identical beams. Deduct the portion cast within the slab depth if the slab volume already includes it.

Why do beams need more steel per cubic metre than slabs?

Beams carry concentrated bending and shear over longer spans, requiring heavier main bars plus stirrups throughout their length, whereas slabs distribute load in two directions with lighter distributed reinforcement.

Does this include formwork?

No. Formwork is measured in area of contact surface, not volume, and is usually priced separately. This calculator covers concrete volume and indicative reinforcement weight only.

Should I use the clear span or the centre-to-centre span?

For concrete quantity, use the clear length of beam actually cast between column faces, and count the column-beam junction once. Centre-to-centre spans overstate the pour. For design, spans are defined by your engineer's own convention, which is a separate question from take-off.

Beam concrete calculator — volume and reinforcement weight

Concrete volume for beams from span, width and depth, multiplied across the number of identical beams, with an indicative reinforcement weight.

beam

Dimensions inyou enter

Number of beamsyou enter

Beam spanyou enter

Beam widthyou enter

Beam depthyou enter

Ordering

Wastage allowanceyou enter

Wastage is site-specific. Order allowance, breakage and cutting loss differ by material, supplier and workmanship; enter your own figure.

Steel intensityyou enter

kg / cu m

Your assumption, used only for an indicative weight. Replace it with a bar bending schedule before ordering.

Result — calculated from your inputs

Concrete to order4.375 cu m

In cubic feet154.50 cu ft

Indicative steel(at the intensity you entered)679.60 kg

Working

Net volume150.00 cu ft

Net volume in cubic metres4.248 cu m

Order volume4.375 cu m

Steel weight679.60 kg

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How this calculator works

volume = count × dimension A × dimension B × dimension C
order  = volume × (1 + wastage %)
steel  = net volume (cu m) × steel intensity (kg/cu m)

You enter: A value you supply. Nothing is assumed for you.
Calculated: Arithmetic on your inputs, shown in the working.
Assumption: A factor or allowance you can change — mix ratios, wastage, dry-volume factors.
Approximation: Geometry or method that approximates reality; labelled wherever used.
Verify locally: Planning parameters, statutory rates and structural design must come from the authority or a qualified professional.

Measure the clear span or the centre-to-centre span consistently

Beam concrete is usually measured centre-to-centre of supporting columns, with the column volume counted separately, or clear span between column faces with the junction counted in the column. Mixing the two conventions double-counts or omits the beam-column junction across the whole building.

Pick one convention, apply it everywhere, and note which one you used. On a frame with many columns the difference is not trivial.

Beam depth is usually below the slab

Where the beam is cast monolithically with the slab, the beam depth entered here should normally be the depth below the slab soffit, because the slab volume already accounts for the top portion. Entering the full structural depth alongside a full slab area counts the overlap twice.

Beams also carry a much higher steel intensity than slabs, driven by span, load and shear reinforcement. The default here reflects that difference but remains an assumption for you to replace.

Worked example

Six beams of 230 mm × 450 mm running 4 m clear are 6 × 0.23 × 0.45 × 4 = 2.484 cubic metres of concrete. With a stated steel intensity of 150 kg per cubic metre the indicative reinforcement is about 373 kg.

Beam steel intensity is typically higher than slab intensity, which is why the two are entered separately rather than averaged.

Mistakes in beam quantities

Measuring the beam depth including the slab it is cast with, then counting that same concrete again in the slab take-off.

Using centre-to-centre spans instead of clear spans between column faces.

Assuming every beam on the floor is identical; enter each distinct size as its own row.

This is quantity only, not design

Beam width, depth, span arrangement and reinforcement are structural design decisions made by a qualified engineer for the specific building. This page multiplies dimensions you were given.

It offers no sizing advice and must not be used to decide a member size.

Frequently asked questions

How do I calculate beam concrete volume?: Multiply span by width by depth for one beam, then by the number of identical beams. Deduct the portion cast within the slab depth if the slab volume already includes it.
Why do beams need more steel per cubic metre than slabs?: Beams carry concentrated bending and shear over longer spans, requiring heavier main bars plus stirrups throughout their length, whereas slabs distribute load in two directions with lighter distributed reinforcement.
Does this include formwork?: No. Formwork is measured in area of contact surface, not volume, and is usually priced separately. This calculator covers concrete volume and indicative reinforcement weight only.
Should I use the clear span or the centre-to-centre span?: For concrete quantity, use the clear length of beam actually cast between column faces, and count the column-beam junction once. Centre-to-centre spans overstate the pour. For design, spans are defined by your engineer's own convention, which is a separate question from take-off.