Mixing concrete isn’t just throwing a bunch of stuff into a wheelbarrow and hoping for the best. It’s all about balance. Too much cement and it’ll crack. Not enough, and it won’t hold. That’s why getting your mix ratio right really matters each job needs a slightly different approach.
You might think concrete is just concrete. But the truth is, it changes depending on what you’re building. From laying a patio to pouring a structural foundation, the ratio of cement, sand, and aggregate plays a big role in how strong, workable, and long-lasting your concrete will be.
First, What’s in a Basic Concrete Mix?
Before we jump into charts and numbers, it’s good to know what’s actually in the mix.
Concrete is made up of:
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Cement (usually Portland cement)
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Sand (fine aggregate)
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Gravel or crushed stone (coarse aggregate)
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Water
Sometimes people throw in additives or admixtures, but at the core, that’s it. The trick is in how much of each you use. That’s what we’re focusing on here.
1. General Purpose Mix: 1:2:3
Let’s start with a standard. If you’re working on a general concrete job say, a garden path or small shed base a 1:2:3 ratio works well.
That means:
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1 part cement
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2 parts sand
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3 parts gravel
It’s a reliable, all-around mix. It’s not overkill, but still solid enough for surfaces that don’t carry a ton of weight.
This mix gives you decent strength without being too hard to work with. If you’re doing something like fence post bases or steps, this is often enough.
2. For Structural Concrete: 1:1.5:3
Now, if you’re putting in foundations or anything that’s going to bear serious load, you want it a bit stronger. That’s where the 1:1.5:3 mix comes in.
Here’s how it breaks down:
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1 part cement
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1.5 parts sand
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3 parts gravel
It’s got more cement in it, which gives you higher strength. Think house foundations, retaining walls, or thick slabs.
You’ll need to be a bit more precise when mixing this one, since it’s less forgiving. But it’s worth it for the added strength.
3. Paving Mixes: 1:2:4 or 1:2.5:3.5
Laying a driveway or paving stones? You’ll want a mix that holds up under weight and weather.
Try:
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1 part cement
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2 to 2.5 parts sand
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4 to 3.5 parts gravel
This mix gives a good balance between strength and workability. It’s not as strong as structural mixes, but for paving that sees light to medium traffic, it works well. Plus, it’s not too stiff to smooth out or level.
4. Mortar Mix (No Gravel): 1:4 or 1:5
If you’re not pouring slabs but laying bricks or blocks, that’s a different game. You don’t need gravel in this case just cement and sand.
Common mortar ratios are:
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1 part cement
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4 or 5 parts sand
This gives you a smooth, workable mix that bonds well with brick. It’s softer than concrete but perfect for binding units together.
For pointing or decorative work, some people even tweak it slightly and add lime. But for most garden walls or brickwork, the standard mix does the job.
5. Kerbs and Edging: 1:2:5
Need to set kerbs or edging stones? You’ll want a strong base that can take occasional knocks and pressure from foot traffic or lawnmowers.
This one’s a bit leaner:
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1 part cement
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2 parts sand
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5 parts gravel
It’s strong but with a little give, so it doesn’t go brittle. It also uses a bit less cement, which is handy if you’re doing a larger stretch and don’t want to burn through materials too fast.
6. C20, C25, C30… What Do Those Mean?
You’ve probably seen mixes like C20 or C25 mentioned online or on bag labels. These are concrete grades based on compressive strength, measured in megapascals (MPa). In short, higher numbers mean stronger concrete.
Here’s a rough guide for what they’re used for:
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C15 (1:3:6) – Paths, garden slabs
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C20 (1:2.5:3.5) – Light-duty floors
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C25 (1:2:4) – Domestic driveways
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C30 (1:1.5:3) – Structural beams, heavy-duty slabs
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C35 and up – Commercial or industrial jobs
These grades are a bit more specific and often used in professional settings where exact strength is needed. But if you’re working on a home project, the part ratios we’ve been talking about will usually be enough.
Mixing by Volume vs Mixing by Weight
Quick note here. All these ratios are based on volume, not weight. So when we say “1 part cement,” we mean one shovel, one bucket, or whatever container you’re using, just be consistent. Don’t switch from scooping cement with a bucket to sand with a shovel.
In more technical or large-scale jobs, people often use weight for accuracy, but for most jobs at home or on-site, volume is the standard.
Water: Don’t Overdo It
It’s tempting to chuck in a bit more water if the mix feels too dry. But hold back. Too much water weakens the concrete. Start small, mix it in well, then add little bits if needed.
You want a mix that holds its shape but is still workable. If it slumps like wet porridge, it’s too loose. If it’s dry and crumbly, add a splash more.
Handy Chart: Concrete Mix Ratios at a Glance
| Use | Cement | Sand | Gravel | Notes |
|---|---|---|---|---|
| General Purpose | 1 | 2 | 3 | Paths, steps, post bases |
| Structural | 1 | 1.5 | 3 | Foundations, load-bearing slabs |
| Paving | 1 | 2–2.5 | 3.5–4 | Driveways, garden paving |
| Mortar (No Gravel) | 1 | 4–5 | – | Brickwork, pointing |
| Kerbs & Edging | 1 | 2 | 5 | Garden edges, light kerbs |
| C20 Grade | 1 | 2.5 | 3.5 | Floors, domestic slabs |
| C25 Grade | 1 | 2 | 4 | Driveways |
| C30 Grade | 1 | 1.5 | 3 | Beams, structural elements |
