Concrete calculator

Work out the concrete for a slab, strip footing or post holes in cubic metres or cubic yards. It adds the 10% extra that MeisterCalc's Concrete calculator adds, and counts premix bags from each maker's stated yield.

Concrete calculator

This calculator needs JavaScript, which is turned off or didn't load. You can still do it by hand: the formulas and worked examples below give the same answers.

Units

Metric (mm, m³) US (ft, in, yd³)

What are you pouring?

Slab Strip footing Post holes

Slab length

Slab width

Slab depth

Count bags of (optional)

Yields from each maker's data sheet, listed under the calculator.

Cost (optional): your price per m³, cubic yard or bag

Price

Your supplier's price, in your currency.

Priced

Rebar for a slab (optional): bars both ways, cover, laps

Uses the slab length and width above. The bar spacing, cover and lap come from your drawings; the numbers here are only the example.

Bar spacing, both ways

Edge cover

Concrete between the bar ends and the slab edge.

Lap where bars join

Only needed when a bar is longer than one stock length.

Stock bar length

Millimetres in, cubic metres and litres out. The same maths as Concrete in the MeisterCalc app, including its 10% extra.

Published 6 November 2026 · By Sai Nath

Worked example: a 4 × 3 m slab, 100 mm thick

Volume: 4.0 × 3.0 × 0.1 = 1.2 m³, which is 1200 litres.
Order with 10% extra: 1.2 × 1.10 = 1.32 m³.
Bags: Boral Concrete Mix 20 kg makes 108 bags to the cubic metre, so 1.32 × 108 = 142.6, rounded up to 143 bags.

In feet and inches, a 12 × 10 ft slab 4 in thick is 40 ft³, or 1.48 cubic yards. With 10% extra that is 44 ft³ (1.63 yd³), or 74 bags of 80 lb at 0.60 ft³ a bag, the yield QUIKRETE prints on its data sheet.

How it works

Slab or footing: length × width × depth, all in metres, gives cubic metres. A strip footing is the same sum with the length of all the runs added up.
Post holes: π × radius² × depth for one hole, times the number of holes.
Order: the volume × 1.10, the 10% extra the app always adds for an uneven base, overpour and waste.
Bags: the order ÷ the yield the maker prints for that bag, rounded up to a whole bag.

Feet and inches are turned into millimetres on the way in, and cubic yards are 0.7646 m³.

Concrete in MeisterCalc

Concrete in the MeisterCalc app

Open Home ▸ Concrete and enter Length 4000 mm, Width 3000 mm and Depth 100 mm on the Slab tab. It shows Volume 1.200 m³, 1200.0 L and Order (+10%) 1.320 m³, with a live drawing of the slab. The Holes tab does post holes from the diameter, depth and count.

On Home, tap Concrete
Enter 4000 × 3000 × 100 mm
Read 1.200 m³

The app version, with every input, result and screen: Concrete in MeisterCalc.

Concrete is one of the three free calculators in the app, with Concrete, Stairs and Check Square: no trial and no account. The others unlock with a one-time purchase, no subscription required, or with a weekly subscription that starts with a 3-day free trial. Every calculation runs on the phone, so it works with no signal on site. It runs on Android 7.0 or later. Get MeisterCalc on Google Play

Questions

How many bags of concrete make a cubic metre?

It depends on the product. Boral Concrete Mix 20 kg: 108 bags. Cement Australia PROStrength 20 kg: about 110. Dricon HandiCrete 25 kg (New Zealand): 100. Read the yield on the bag you buy.

How much concrete is in one post hole?

π × radius² × depth: a hole 300 mm across and 800 mm deep holds 0.0565 m³, or 56.5 litres. Six of them come to 0.339 m³, or 0.373 m³ with 10% extra.

How many cubic yards is a cubic metre?

1 m³ is 1.308 yd³, and 1 yd³ is 0.765 m³, or 27 ft³.

Does it tell me how thick the slab should be?

No. The thickness, reinforcement and footing sizes come from the engineer's drawings, the building code and your council. The calculator works out the volume for the size you enter.

Sources

Building rules are set by the National Construction Code, the NZ Building Code or the Approved Documents and by your council, not by this page or the app.

Concrete calculator