Concrete Cube Calculator: Nail Your Mixes and Never Guess a Pour Again
Ever turned up to site and realised you’ve got enough concrete for a small patio, but not enough for all your test cubes? Or worse, you’ve made up the right number of cubes, but can’t remember if you did them at 100mm or 150mm sides. Concrete cube calculators exist for a reason: so you don’t end up on your knees, scraping the last mix out of the drum, or explaining to the boss why there’s an empty spot in the curing tank.
In this guide, I’ll show you how to use a concrete cube calculator, why the size and number of cubes matter, and a few tricks to make sure your results are spot-on (and you don’t get a fail on test day).
What’s a Concrete Cube Calculator (and Why Should You Care)?
A concrete cube calculator is your shortcut to getting the right volume for test cubes—those little blocks you cast to check if your concrete is up to scratch. Think of it as your recipe card for concrete quality control. If you get the maths wrong, you either waste concrete (like making too many sausage rolls for a party) or, even worse, run short and can’t do all your required tests.
Cube moulds come in standard sizes: typically 100mm x 100mm x 100mm (4in x 4in x 4in) or 150mm x 150mm x 150mm (6in x 6in x 6in). The calculator tells you exactly how much wet concrete you’ll need to fill however many cubes you’re making. Simple, but crucial.
Why Concrete Cube Testing Matters
Here’s the bit most people get wrong: cube tests aren’t just a box-ticking exercise. They’re your only real proof that the mix you’ve poured is strong enough for its job—whether that’s holding up a new house or just a garden path. Skip the test or fudge the numbers and you’re building on sand, not stone.
How to Use a Concrete Cube Calculator (With a Worked Example)
Let’s run the numbers—no guessing, no sleepless nights. We’ll do it in both metric and imperial units, so nobody’s left scratching their head.
Say you need to make 6 cubes for your test, using 150mm (6in) moulds.
Step 1: Calculate the Volume of One Cube
- Metric: Volume = Length x Width x Height = 0.15m x 0.15m x 0.15m = 0.003375m³
- Imperial: Volume = 6in x 6in x 6in = 216in³
- To convert to cubic feet: 216in³ ÷ 1,728 = 0.125ft³
Step 2: Multiply by Number of Cubes
- Metric: 0.003375m³ x 6 = 0.02025m³
- Imperial: 0.125ft³ x 6 = 0.75ft³
Step 3: Add a Bit for Wastage (the Spare Teabags Principle)
No one ever regrets having a bit more. Add 10% for spillage, air pockets, and the fact you’ll never get it all out of the mixer:
- Metric: 0.02025m³ x 1.10 = 0.0223m³
- Imperial: 0.75ft³ x 1.10 = 0.825ft³
So, for six 150mm (6in) cubes, you’ll need about 0.022m³ (0.825ft³) of fresh concrete mix. If you’re using 100mm (4in) cubes, the numbers drop to about 0.011m³ (0.39ft³) for six.
If you want a shortcut, use this concrete volume calculator to take the donkey work out of it—just remember to put in the cube dimensions and number required.
How Many Cubes, and How Big?
Bet the merchant never told you this: the number of cubes you need isn’t set in stone (pun intended). For most site pours, you’ll cast either three or six cubes per sample. Three get crushed at 7, 14, and 28 days, or sometimes all at 28 days if you’re in a hurry. Some specs want more cubes for extra testing or backup.
And don’t get caught out by the size—100mm (4in) cubes are common for routine mixes, while 150mm (6in) cubes are used for higher-grade concrete or structural work. Check your spec sheet before you start mixing.
The Most Common Mistakes (and How to Dodge Them)
- Not allowing for wastage: Ordering bang on is like buying exactly enough wallpaper with zero offcuts. You’ll run short.
- Mismatched units: Measuring your cubes in mm and your mix in ft³ is like making a pie in Celsius and baking it in Fahrenheit.
- Forgetting to cure cubes properly: If you dry them out, your results are useless.
- Not recording mould sizes: You’ll look a right muppet at test time if you don’t know whether you used 100mm or 150mm cubes.
For more awkward-shaped pours (like steps, ramps, or slabs), a concrete steps calculator is your best mate—it does the heavy lifting so you don’t have to.
Quick Reference Table: Cube Volumes
| Cube Size | Volume per Cube (m³ / ft³) | 6 Cubes (m³ / ft³) | 10% Wastage (m³ / ft³) |
|---|---|---|---|
| 100mm (4in) | 0.001m³ / 0.035ft³ | 0.006m³ / 0.21ft³ | 0.0066m³ / 0.23ft³ |
| 150mm (6in) | 0.0034m³ / 0.125ft³ | 0.020m³ / 0.75ft³ | 0.022m³ / 0.83ft³ |
Real-World Tips for Cube Testing
- Always oil your moulds before pouring—concrete sticks like gum to a boot otherwise.
- Tap or vibrate the moulds to get rid of air bubbles.
- Label each cube properly—date, mix, pour location, and cube size. No scribbling on the back of a fag packet.
- Cure cubes by submerging in water or using damp hessian—don’t let them dry out.
And if you’re casting cubes alongside a tricky pour (like steps or odd shapes), just chuck those extra dimensions into the concrete steps calculator and save your head from spinning.
Questions people are actually asking
How much concrete per cube?
For a standard 150mm x 150mm x 150mm (6in x 6in x 6in) cube, you need 0.003375m³ (0.125ft³) of concrete. For a 100mm (4in) cube, it’s 0.001m³ (0.035ft³). Don’t forget to add 10% for wastage.
How many concrete cubes per cubic metre (or cubic yard)?
One cubic metre (1.31 cubic yards) of concrete will make about 296 cubes at 100mm (4in), or about 89 cubes at 150mm (6in). But unless you’re running a testing lab, you’ll never need that many in one go!
How many concrete test cubes should I take?
Most site specs call for at least three cubes per test—one for each of 7, 14, and 28 days. Some jobs (especially structural work or high-spec projects) require six cubes or more, to allow for backup tests.
How many cubes of concrete fit in a truck?
A typical ready-mix lorry carries 6 to 8 cubic metres (7.8 to 10.5 cubic yards) of concrete. If you turned the whole load into 150mm (6in) cubes, that’s over 1,700 cubes—enough to fill a decent-sized skip (dumpster) and give the lab nightmares.
How long should concrete cubes be cured?
Concrete cubes are usually cured for 7, 14, and 28 days before testing. The 28-day strength is the main benchmark, but early tests can spot problems sooner. Always keep cubes moist—dried-out cubes are like stale bread: useless for testing.
How much does concrete cube testing cost?
Prices vary by country and lab, but you’ll usually pay per cube tested. Cost covers sample pickup, curing, and crushing. Always check with your local lab for up-to-date rates.
How many days can concrete cubes be cured before testing?
Standard practice is to test at 7, 14, and 28 days, but cubes can be kept and tested later if needed—some projects specify longer-term tests at 56 or even 90 days for high-performance mixes.
Conclusion: Don’t Guess—Calculate
Ordering concrete for test cubes shouldn’t feel like a lucky dip at the village fête. Get your volumes right with a concrete volume calculator, allow for wastage, and make sure you’re casting enough cubes for every test required. Trust me—nobody has ever finished a job wishing they’d made fewer cubes.
Ready to take the guesswork out of your next pour? Give our concrete steps calculator a go and banish the mental arithmetic for good.
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 Post Calculator — work out exactly how much you need and what it will cost.
- Concrete Steps Calculator — get an instant materials estimate for your project.
- Concrete Weight Calculator — size up quantities and costs before you head to the merchant.
- Concrete Mix Calculator — plan your order so you avoid over- or under-buying.
Explore every free calculator on HowMuchDoINeed — no sign-up required.