Concrete mix grades in the M-series run from M10 (roughly 1450 PSI / 10 MPa) to M40 (5800 PSI / 40 MPa) and beyond. Each grade specifies a characteristic compressive strength at 28 days and a corresponding cement:sand:aggregate ratio. Choose the wrong grade and your structure either fails under load or wastes money on over-engineered concrete.
How mix ratios work — and what the M-number actually means
The M in M10, M20, M30 stands for mix. The number is the characteristic compressive strength in MPa (megapascals) measured on a 150 mm cube sample at 28 days. M20 = 20 MPa, which is the minimum grade permitted by most codes for reinforced concrete structural members.
The nominal mix ratio is expressed as cement : fine aggregate (sand) : coarse aggregate by volume. For M20 the nominal mix is 1:1.5:3, meaning 1 part cement, 1.5 parts sand, 3 parts aggregate. As grade increases, the cement content rises relative to aggregate, which increases strength and cost simultaneously.
Use the concrete mix ratio calculator to convert any M-grade into actual batch weights per cubic metre or cubic yard — accounting for the specific gravities of your materials.
M10 to M40 mix ratios, PSI equivalents, and typical applications
| Grade | Ratio (C:S:A) | MPa | PSI (approx.) | Typical use |
| M10 | 1 : 3 : 6 | 10 | 1,450 | Lean concrete, blinding, mass fill |
| M15 | 1 : 2 : 4 | 15 | 2,175 | Plain footings, non-structural slabs |
| M20 | 1 : 1.5 : 3 | 20 | 2,900 | Residential RCC slabs, beams, columns |
| M25 | 1 : 1 : 2 | 25 | 3,625 | Heavy slabs, commercial foundations |
| M30 | Design mix | 30 | 4,350 | Bridges, water-retaining structures |
| M35 | Design mix | 35 | 5,075 | Prestressed members, marine structures |
| M40 | Design mix | 40 | 5,800 | High-rise columns, pre-cast elements |
Grades M10 to M20 use nominal mixes — fixed volumetric ratios that provide adequate strength for most residential work. M25 and above technically require design mixes, where the w/c ratio, aggregate grading, and admixture dosage are calculated from trial batches to hit a target mean strength that accounts for statistical variability.
PSI vs MPa: converting between systems
1 MPa = 145.04 PSI. To convert MPa to PSI, multiply by 145. To go the other way, divide PSI by 145. In US construction, 3,000 PSI (≈ 20.7 MPa) is the standard residential concrete specification — directly equivalent to M20. 4,000 PSI (≈ 27.6 MPa) maps closely to M25–M30. The concrete PSI to MPa converter handles both directions instantly.
UK and Australian standards use C-grades (C20, C25, C30 etc.) which express the characteristic cylinder strength in MPa — the cylinder test gives results roughly 80% of the cube test, so C25 ≈ M30 in terms of actual performance. Do not treat C-grades and M-grades as interchangeable without checking which test method the specification references.
Common mistakes when specifying or batching mix ratios
Using nominal ratios above M25. M30 to M40 concrete cannot reliably achieve target strength through fixed volumetric ratios. The cement content needs to be determined from water-cement ratio calculations and material-specific trial mixes. Using 1:0.75:1.5 as a ‘nominal M30’ is likely to undershoot or overshoot depending on aggregate moisture and grading.
Not adjusting for aggregate moisture. Aggregate stockpiles typically carry 2–6% free moisture. If you add design water without subtracting moisture already present in the aggregate, you raise the effective w/c ratio and reduce strength — often by one full M-grade. Weigh wet and dry samples to determine free moisture before batching.
Confusing M-grade with 28-day mean strength. The M-number is the characteristic strength, meaning 95% of test samples should meet it. The target mean strength used in mix design is typically M + 1.65σ, where σ is standard deviation. For M20 with a 4 MPa SD, target mean strength is 20 + 6.6 = 26.6 MPa. Mixing to exactly M20 will fail about 50% of tests.
Using dry-volume ratios for bagging calculations. The dry ingredients occupy roughly 30–35% more volume than the finished concrete due to compaction. 1 m³ of M20 concrete requires approximately 1.54 m³ of dry mix. Ignoring the bulking factor leads to under-ordering materials by a third.
Related calculators you might need
Once you have your mix grade, the next step is quantifying materials. The cement quantity calculator outputs bags of cement per m³ for any M-grade. If you are batching on site rather than ordering ready-mix, the concrete batch calculator converts your mix design into exact weights per batch. For the water side of the equation, the water-cement ratio calculator lets you determine the precise w/c ratio for your target strength. If you are adding plasticisers or retarders to extend workability at higher grades, the concrete admixture dosage calculator converts manufacturer-recommended percentages into actual dosing volumes per m³.
Frequently asked questions
What is the difference between M20 and 3000 PSI concrete?
M20 has a characteristic compressive strength of 20 MPa, which equals 2,900 PSI. US residential specs typically call for 3,000 PSI (20.7 MPa). The difference is less than 4% and falls within normal test variability — for practical purposes they are the same grade. If a US specification calls for 3,000 PSI and you are sourcing locally specified M20 mix, verify with your engineer that the characteristic strength approach aligns with the project’s acceptance criteria.
What mix ratio should I use for a driveway?
A residential driveway requires a minimum of M25 / 3,500 PSI — M20 is marginal for vehicle loads and will surface-scale faster under freeze-thaw. The ratio for M25 is approximately 1:1:2 (cement:sand:aggregate) as a nominal mix. Air entrainment is essential in freeze-thaw climates. Use the concrete mix ratio calculator to get precise batch weights for your site.
Can I use M10 for a concrete slab?
M10 (10 MPa / 1,450 PSI) is suitable only for blinding layers and non-structural mass fill. It should not be used for any slab that carries foot traffic, furniture, vehicles, or structural loads. For a basic residential floor slab, the minimum is M20; for garage slabs or any slab carrying vehicles, M25 is the appropriate starting point.
What does ‘design mix’ mean for M30 and above?
A design mix is produced through laboratory trial batches that account for the specific gravity, absorption, and grading of your local aggregates, the cement brand’s actual strength contribution, and the required workability. Rather than a fixed ratio, a design mix specifies a maximum water-cement ratio, a minimum cement content per m³, and a target slump. Ready-mix plants supply design mixes as standard; on-site batching at M30+ requires mix design documentation from a materials lab.
How much does mix grade affect cost?
Each grade increase from M20 to M25 typically adds 8–12% to material cost due to higher cement content. M30 costs roughly 20–25% more per m³ than M20. Labour and delivery costs are unaffected by grade. The largest cost driver above M30 is usually the requirement for admixtures — superplasticisers to maintain workability at low w/c ratios add £5–£15 / $8–$20 per m³ depending on dosage rate.
Is M25 the same as C25?
No. M25 specifies a 25 MPa characteristic strength on a 150 mm cube. C25 specifies a 25 MPa characteristic strength on a 150 mm cylinder. Cylinder strengths run approximately 80% of cube strengths, so C25 ≈ M31 in equivalent cube strength terms. UK structural drawings specify C-grades; Indian and many Asian standards use M-grades. Always confirm which test geometry the project specification references before sourcing concrete.
Concrete is the most widely used building material on Earth, yet some of the most important decisions behind it are still made with rough guesses, outdated spreadsheets, and conflicting advice from random websites.
We thought that was a problem worth fixing.
Every calculator and guide on this platform exists for one reason: to replace uncertainty with reliable numbers. Whether you’re estimating a slab, planning footings, calculating reinforcement, comparing mix designs, or budgeting a project, the goal is the same—help you make decisions with confidence before concrete is poured.
We don’t publish calculators for the sake of having calculators. Every formula is researched, tested, and built around real construction requirements. Every guide is written to answer practical questions that contractors, builders, engineers, and homeowners actually face on job sites—not questions invented for search engines.
Because concrete is unforgiving.
A small mistake in volume estimation can waste thousands of dollars. An undersized footing can create structural problems. Incorrect reinforcement calculations can compromise performance. Once concrete is placed, many mistakes become expensive—or impossible—to undo.
That’s why accuracy matters.
Our approach is simple: start with the engineering, verify the calculations, explain the reasoning, and present the results in a way that anyone can use. No inflated claims. No copied content. No generic formulas stripped of context.
Just practical tools, clear guidance, and calculations designed to solve real-world construction problems.
The internet has plenty of articles about concrete.
We’re building a resource that helps people work with it.