Concrete Slab Calculator: Get Your Pour Right First Time (No Guesswork, No Panic Orders)

Paving & Groundwork

Concrete Slab Calculator: Get Your Pour Right First Time (No Guesswork, No Panic Orders)

Graham howmuchdoineed · 27 July 2026 · 6 min read

Ever got halfway through a pour, only to realise you're a wheelbarrow short and the lorry's already rinsing out? Yeah, we've all been there—the builder's equivalent of running out of tea bags mid-cuppa. In this guide, you'll learn how to calculate exactly how much concrete you need for any slab, pad or floor—whether you're working in metres (m³) or cubic feet (ft³), kilograms or pounds, pounds or euros. No more panic mixes or last-minute dashes to the yard.

Why You Need a Concrete Slab Calculator (and Not Just a Wild Guess)

Here's the bit most people get wrong: concrete isn't as forgiving as your gran's sponge cake recipe. Undercook it (order too little), and your job stalls. Overdo it (order too much), and you're left with a mini Stonehenge of wasted mix in the driveway.

A concrete volume calculator takes the guesswork out, so you're not measuring in 'about right' or 'looks enough'. It's like shopping with a list—not just grabbing whatever's on offer and hoping for the best.

The Basics: How to Calculate Concrete for a Slab or Pad

Bet the merchant never told you this: the formula for slab volume is dead simple. It’s:

Volume = Length × Width × Depth

But here’s where most jobs trip up—mixing units. If your tape’s in feet but your supplier wants metres, it’s a recipe for chaos. Always use consistent units, and keep both metric (metres, litres, kilograms) and imperial (feet, cubic yards, pounds) handy.

For a rectangular slab:

Metric: Volume (m³) = Length (m) × Width (m) × Depth (m)
Imperial: Volume (ft³) = Length (ft) × Width (ft) × Depth (ft)

To get cubic yards (US), divide the total cubic feet by 27. To get litres, multiply m³ by 1,000.

Worked Example: Concrete Slab for a Shed Base

Let’s say you’re pouring a shed base. The size: 3m x 4m (10ft x 13ft), at 100mm (4in) thick.

Metric:
- Length: 3m
- Width: 4m
- Depth: 0.1m (100mm)
- Volume = 3 × 4 × 0.1 = 1.2m³
Imperial:
- Length: 10ft
- Width: 13ft
- Depth: 0.33ft (4in)
- Volume = 10 × 13 × 0.33 ≈ 42.9ft³
- In cubic yards: 42.9 ÷ 27 ≈ 1.6yd³

Now, add 10% for wastage—the insurance policy against spillages, mis-shapes, or that mate who can’t keep a shovel steady. So order:

1.2m³ × 1.10 = 1.32m³
1.6yd³ × 1.10 = 1.76yd³

If you want to skip the maths and just plug in your dimensions, our concrete slab calculator does it for you in seconds—no calculator app, no scribbling on offcuts.

Unit Conversions: Mixing Metres and Feet Is Like Mixing Vodka and Milk

1m = 3.28ft
1m³ = 35.3ft³ = 1.31yd³ = 1,000 litres (264 US gallons)
25kg bag (55lb) of ready-mix covers ≈ 0.011m³ (0.39ft³)

So if you end up with a total volume, you can work out how many bags you’ll need—or, if it’s a big job, how many cubic metres/yards to order from the plant.

Concrete Slab Costs: How Much Is This Actually Going to Set You Back?

This is the question everyone asks: “How much does a concrete slab cost?”

Well, it depends—on location, thickness, finish, access, and whether you’re mixing by hand or getting a wagon in. Here’s a rough breakdown (currency-neutral):

Item	Unit	Typical Range (UK/EU/US/AU)
Ready-mix supply	per m³ (yd³)	£80-£150 / $100-$200
DIY bagged mix	per 25kg (55lb)	£4-£8 / $5-$10
Labour (pro)	per m² (ft²)	£30-£50 / $40-$60
Total slab (materials + labour)	per m² (ft²)	£50-£120 / $60-$130

Remember, these are ballparks. For the Philippines, prices vary but tend to be lower—always check locally.

No matter where you’re working, use the concrete volume calculator to get an accurate material estimate before ringing the merchant or the batching plant.

Don’t Forget: Wastage, Site Conditions, and That One Corner That’s Never Square

Wastage: Always add 10% unless you fancy running out right at the awkward bit.
Site access: If you can’t get the truck near, you’ll need to factor in pump hire or more labour.
Thickness: Don’t skimp—most slabs need at least 100mm (4in) for sheds, 150mm (6in) for driveways.
Reinforcement: Mesh, fibres or bars may be needed (not included in concrete volume, but don’t forget them).

Skip the guesswork and get your numbers right with the concrete slab calculator. It’s the difference between a smooth job and a sweaty phone call to the yard while the mix goes off.

Questions People Are Actually Asking

How much does a concrete slab cost?

Concrete slab cost depends on size, thickness, location, and whether you DIY or hire it out. For a basic slab, expect £50–£120 per m² (about $60–$130 per 10.8ft²) all-in for materials and labour. Large pours and special finishes cost more.

How much concrete do I need for a slab?

Multiply length × width × depth (all in the same units) to get volume. Add 10% for wastage. Or just use the concrete slab calculator to get the answer with zero fuss.

How much does a concrete slab cost in the Philippines?

Prices in the Philippines are generally lower than in the UK or US, but vary by region, supplier, and finish. As a ballpark, expect ₱2,000–₱4,000 per m³ (about $35–$70 per m³), including materials and basic labour. Always get local quotes.

How much does concrete slab installation cost?

Installation adds labour—usually £30–£50 per m² ($40–$60 per 10.8ft²) depending on your area, access, and finish. The total installed cost is the sum of materials and labour.

How much concrete is needed for a pad or floor?

Same as a slab—multiply length × width × thickness, and convert to cubic metres or cubic yards as needed. For a quick answer, try the concrete volume calculator.

How much is concrete slab per square foot?

Expect to pay $6–$12 per square foot (about £50–£120 per m²) for a finished, installed slab. Materials alone are less, but don’t forget prep, reinforcement, and finishing.

How many bags of concrete do I need for a slab?

Divide your total volume by the yield per bag (usually 0.011m³ or 0.39ft³ for a 25kg/55lb bag). For example, a 1m³ (35.3ft³) slab needs about 91 bags. Or just use the calculator and let it do the maths.

Conclusion: Pour Once, Not Twice—Get Your Numbers Right

Ordering concrete without a proper calculation is like showing up to site with no boots and hoping nobody notices. Save yourself the drama (and the extra trip to the merchant) by letting the concrete slab calculator do the hard bit. Accurate, quick and in both metric and imperial—so you can get on with the pour, not the paperwork.

Free tools to put this into practice

Reading is one thing — working out your own numbers is what saves time and money. Here are the free HowMuchDoINeed calculators that pair best with this guide:

Concrete Footing Calculator — work out exactly how much you need and what it will cost.
Concrete Mix Calculator — get an instant materials estimate for your project.
Concrete Cost Calculator — size up quantities and costs before you head to the merchant.
Concrete Steps Calculator — plan your order so you avoid over- or under-buying.

Explore every free calculator on HowMuchDoINeed — no sign-up required.