What concrete mix ratio should you use?

Whether you’re laying a garden path or pouring the footings for a home extension, having the right concrete mix ratio provides you with the foundations for your project. There are lots of factors that go into deciding what ratio is best, as they all contribute to the strength, durability and workability of the concrete. 

In this guide, we’re going to cover everything to do with concrete mix ratios — breaking it down by the type of project they might be used for, and the different concrete grades.

Understanding concrete mix ratios

Essentially, concrete mix ratios tell you how much cement, sand and aggregate to combine to get the result you want. The ratio matters because adjusting each element changes the final qualities of the concrete. Adding more cement generally increases strength, and too much sand can make the concrete easier to work with but reduce its durability. For example, a 1:2:3 ratio would mean:

• 1 part cement
• 2 parts sand
• 3 parts aggregate

Mix ratios can also be measured in two ways:

• Volume
• Weight

For DIYers, it’s usually easier to measure by volume as you can use buckets or shovels as units. Commercial projects tend to use weight-based batching so they can be precise with measurements and stay consistent.

There’s no universal best mix when it comes to concrete mix ratios. It’s all about the best mix for your purpose. Too much cement can be costly; too much sand can lower the strength of the concrete; and using not enough aggregate can cause shrinkage and cracks. 

Commonly used concrete mix ratios (by application)

As we’ve covered briefly, different projects call for different characteristics in their concrete, and that all comes down to the mix ratio. Below, we’ll look into the most widely used ratios and how they’re tailored for specific applications, from general-purpose to heavy-duty builds.

General purpose mix (1:2:3)

This is an all-rounder mix that consists of one part cement, two parts sand, and three parts coarse aggregate. It has a good balance between strength and workability, making it ideal for a range of projects such as:

• Garden slabs
• Footpaths
• Patios

Structural mix (1:1.5:3)

When you’re building something that bears heavy weight, you need a higher-strength mix. Reducing the sand and keeping the coarse aggregate the same improves the concrete's compressive strength by creating a mix that’s denser and more durable. This mix is generally good for:

• Driveways
• Residential buildings

Mass concrete (1:3:6)

Not all concrete applications require high strength. In cases where large volumes are needed, but not necessarily the demand for structural performance, a mass concrete mix might be better suited. In this mix, a higher proportion of sand and aggregate is used compared to cement. This type of mix is usually ideal for non-load-bearing applications, such as:

• Minor landscaping
• Levelling courses

Using ballast (1:5 or 1:6)

Ballast is a pre-mixed blend of sand and aggregate, often used to simplify the concrete mixing process. As it pre-mixes two of the elements in a concrete mix, it reduces the need to measure separate materials. It’s usually great for the following projects:

• Shed bases
• Path edges
• Fence posts

Standardised concrete mix ratios by grade

Concrete is graded based on its compressive strength reached after 28 days, which is often measured in newtons per square millimetre (N/mm²) or megapascals (MPa). These grades are vital when following building regulations, using ready-mix, or needing reliable strength. Let’s have a look at some of the most common types of concrete grades and what they’re used for:

What is C20 concrete mix ratio (1:2:4)

Often referred to as Gen 3 and is not suitable for load-bearing structures because of its lower compressive strength compared to other mix ratios. Some characteristics of the C20 mix are:

• Strength: 20 N/mm²
• Uses: Light-duty construction projects like bases for sheds & garages, and also paving. 

What is C25 concrete mix ratio (1:1:2)

Best for foundation work and some structural elements in houses due to its great balance of strength and workability. The characteristics of the C25 mix are:

• Strength: 25 N/mm²
• Uses: Footings, foundations, reinforced bases, residential builds.

What is C30 concrete mix ratio (1:2:3)

The C30 mix has a higher compressive strength and can withstand high foot traffic and tough weather conditions. It’s ideal for surfaces that need toughness, especially outdoors:

• Strength: 30 N/mm²
• Uses: External slabs, pavements, driveways, and commercial flooring.

What are the types of concrete and their use cases?

Concrete isn’t just about grades and ratios. It’s also about composition and purpose. From weather resistance to structural support, there are many different types of concrete that are engineered to meet the specific demands of any project. 

So, if you’re working with exposed surfaces or high-traffic areas, there’s a type for your task. Here’s a breakdown of the most widely used types of concrete and where they work best.

GEN Concrete (e.g., GEN3)

GEN concrete is used for general, non-structural applications. It typically has a strength of around 20 N/mm², making it suitable for projects where high load-bearing isn’t required. You’ll often find GEN3 used in domestic flooring, shed bases, and shallow foundations.

RC (Reinforced Concrete)

RC, or reinforced concrete, is strengthened with steel bars or mesh to improve its load-bearing capacity and resistance to cracking. The strength of RC depends on the mix ratio used, but it’s great for working with beams, columns, and retaining walls.

PAV Concrete

PAV concrete is specifically designed to withstand freeze-thaw cycles and regular surface wear, due to its added air bubbles, a low water-cement ratio, and strong aggregates that help prevent cracking and damage. It’s a go-to choice for areas like driveways, roads, and pavements.

FND Concrete

FND concrete is a sulphate-resistant mix used in environments where the soil contains high levels of sulphates, which can degrade standard concrete over time. This type of concrete contains less tricalcium aluminate (C₃A), which means the FND concrete becomes less chemically reactive, making it great for use in areas where soils or groundwater have a high sulphate content

Fibre-Reinforced Concrete

Fibre concrete includes added synthetic or steel fibres to help control cracking and shrinkage. The fibres improve toughness and impact resistance, making it ideal for industrial floors, roadways, and areas that experience heavy loading.

Flowable Concrete

Also known as self-compacting or flowable fill, this type of concrete is designed for high workability, meaning it can easily flow into complex spaces without the need for vibration or tamping. Usually, this type of concrete is used for encasing pipes and filling trenches or voids.

Foamed Concrete

Foamed concrete is a lightweight, cellular material made by introducing air bubbles into the mix. It’s used when lightweight materials and heat insulation are both needed, such as when filling gaps or insulating under floors.

DIY vs ready-mix: What should you choose?

The decision on whether to mix concrete by hand or use ready-mix concrete depends on the size of your project, the tools available, and your experience. In this section, we’ll share a few tips on when we think it’s best to use hand-mixing or ready-mixes.

When to use hand-mixing

If you’re working on a small-scale project, like setting fence posts or building a garden path, then hand-mixing can be a cost-effective and convenient way, as it allows you to control the batch size so you can only mix what you need.

When to use ready-mixes

Ready-mixes are usually beneficial for anything that requires structural integrity, like foundations, reinforced slabs, or driveways. The three things that might sway you towards this type of mix are precision, consistency and quality control. 

Final tips for selecting the right mix

Don’t forget, choosing the right concrete mix isn’t about following a formula. It’s about matching the material to the demands of your project. Here are some of our summarised tips that we’ve touched on throughout the blog:

• Match the ratio to the job: Consider the load, exposure, and environmental conditions.
• Avoid overwatering: Too much water may make mixing easier, but it weakens the final product. Aim for a smooth, workable consistency.
• Think about admixtures: For better crack resistance, faster curing, or weather protection, additives like plasticisers, fibres, or air entrainers can make a difference.

Ready to mix with confidence?

Now that you’ve got a solid understanding of concrete mix ratios, you’re better equipped to take on your next project. If you’re considering some performance enhancers for your concrete mixes, then why not take a look at our range of high-quality admixtures? If you need expert guidance or recommendations for your project, then don’t hesitate to contact us today.