Concrete Proportion and Mixture Ratio

Concrete is one of the most simple and best known building materials and probably the most vital for the strength of the constructions of your building, parking lot, patio, garden wall, paths etc. That is why it is important to know how to properly mix and pour concrete.

Concrete contains only the following ingredients: cement (Portland), gravel, sand and water. When cement is mixed with water a chemical reaction takes place. The cement does not simply “dry” it reacts with the water binding the materials in a concrete mix firmly together and harden into an incredibly strong rock like mass.

Gravel and sand are called also aggregate and all you need to know how to mix concrete properly is the correct aggregate to cement ratio. The more cement the stronger the concrete.

The strength of a concrete mix is measured in grades. There are different concrete grades for example C15, C20, C25. The grade of the concrete means the concrete compression resistance after 28 days. It is done in Newtons per square millimetre. A concrete of Grade C15 means that the concrete will have a compresion resistance (withstanding a compression) of 15 N/mm2 per square millimetre in 28 days.


Proportions for different grades:

Cement  :  Sand  :  Gravel
   1    :   2    :    5     for grade C15(general purpose concrete)
   1    :   2    :    4     for grade C25(strong)
   1    :   2    :    3     for grade C30(very strong)

Remember the proportion is done in terms of volume. This means the above proportions are correct if using the same measure.

For example: 1 bucket cement + 2 buckets sand + 5 buckets gravel

Simple Calculation for 1 cubic meter of Concrete

Mixture of half cubic meter sand, one cubic meter of gravel and a portion mix of cement (for the required strength of the concrete) plus water, there will be about one cubic meter of volume


For example:
0.5m³ sand + 1m³ gravel + 8 bags x 50kg cement + water = 1m³ Concrete C25 grade

Volume measures for cement, gravel and sand:
Cement (Portland): 1506 kg per cubic meter (
Gravel (loose, dry): 1522 kg per cubic meter
Sand (dry): 1602 kg per cubic meter

Pressure calculators: 1 Newton (N)= 0.1019716 Kg force
1 Pascal = 0.1019716 Kg/m2= 1 N/m2
1 Megapascal = 101971.6 Kg/m2 = 0.1019716 kg/mm2 = 1 N/mm2
1 Megapascal = 145.0377 psi = 10.19716 kg/cm2

The usual required strenght of the concrete are:
For C30: 30 Megapascal(N/mm2)=4351 psi = 305 kg/m2;generally 4500 psi
For C25: 25 MP (N/mm2) = 3625 psi = 255 kg/m2; generally 4000 psi
For C20: 20 MP (N/mm2) = 2900 psi = 203 kg/m2; gen. 3000 psi
For C15: 15 MP (N/mm2) = 2175 psi = 152 kg/m2; gen. 2000 psi

Another factor which determines the strength and hardness of the finished concrete product is proper mixing of the ingredients. If the ingredients are not thoroughly mixed there will be differing degrees of hardness in various parts of the finished product. Needless to say this is something to avoid at all costs.

Cement can be mixed by hand by a reasonably fir person, by a cement mixer or it can be ordered to be delivered ready mixed.
Mixing concrete by hand is exhausting and can be done only for small quantities - max. 1 cu. metre. For larger projects it is better to be be delivered ready to your site.


While it is very easy to order concrete you have to know what to oder:
- how much concrete (how many cubic metres)
- what grade
- time of the delivery

Once you have the concrete is delivered you have to be prepared to handle it. You should also consider access for the lorry, and you should be aware that the driver won’t be willing to wait long. That is why you should be fully prepared for the concrete also considering that concrete is getting hard pretty fast and you will not have more than 1-2 hours to handle it

How to mix concrete by hand

1. Select mixture formula from the table above. A 1:2:3 (cement:sand:gravel) is also a bullet proof formula.
2. Use a shovel to mix to ingredients in a wheelbarrow or on a large plate of sheet iron on the ground.
3. Add some water and continue mixing by hand. Use minimum volume of water possible. The less water the stronger the concrete.
4. While keeping water minimal be sure that there are no dry areas in the mix
5. Work fast as concrete dries out fast.

Tip

• You can also buy pre-mixed bags of ready-to-mix concrete at DIY supermarkets and lumber yards. These require water and mixing; the measuring is already done for you.
• If you have doubts about your ability to “work” and “finish” concrete, hire professionals. Any job over a few square feet in size may be more than the average homeowner wants to tackle.

Concrete Thickness

Recommended minimum thickness of the concrete for the following projects are:

• Footpaths - 75mm (3 inches)
• Patio - 100mm (4 inches)
• Driveways and Parking areas - 125mm (5 inches)
• Base of light structures - 75mm (3 inches)

Slope of the concrete

Water will gap in depressions without a slab and if there is no natural slab of the land it should be calculated.
Any concrete against a building or a garden wall must slope away from it. Here the reccomended slopes:

• Footpaths - minimal, just to avoid areas where rain water will collect
• Patio - 1:60 (16mm in 1 metre, 5/8in in 3 ft)
• Driveways and Parking areas - 1:40 to 1:60 (25mm to 16mm in 1 metre, 1in to 3/8in in 3ft)
• Base of light structures - 1:80 (12.5mm in 1 metre, ½in in 3 ft)

See full Metric system conversion tables (opens new window)

For further reading:
- Concrete mixing on DIYdata.com
- Mixing concrete on DIYdoctor.org.uk

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