A mix ratio describes how ingredients are divided. Start with the ratio in your project specification, then use the examples below to follow how a measured volume becomes material quantities.
01
Read the parts before doing the maths.
For a cement-to-sand ratio of 1:4 by volume, the total is five parts. Cement takes one fifth of the dry ingredient volume and sand takes four fifths. The parts describe a proportion, not a bag count.
Cement1 part
:
Sand4 parts
5 parts in total
Ingredient volume = total dry volume × ingredient parts ÷ total parts.
Why is there a dry-volume factor?
The examples convert a finished wet volume into an allowance for loose dry ingredients before dividing it into shares. The factor is an assumption you can change in the relevant calculator. Match it to the project information; the example values are not universal constants.
02
Follow an example for the work you are measuring.
Each example starts from a different measured basis. Check that basis first, then apply the specified proportions. Wastage and purchase rounding come afterwards.
Brickwork mortar
Use this after subtracting the solid bricks from the masonry volume to find the wet mortar between them.
1 : 6
Cement : Sand · by volume · example dry factor 1.33
Calculation
Ingredient volume = wet mortar × dry-volume factor × ingredient part ÷ total parts.
Worked example
For 0.30 m³ wet mortar, a 1.33 dry factor gives 0.399 m³ dry ingredients. At 1:6, cement is 0.057 m³ and sand is 0.342 m³ before wastage.
Check before using this example
The displayed ratio is only a starting point. Check it against the project specification, brick type and site practice.
Ratio parts are measured by volume.
Wet mortar is found by subtracting solid brick volume from masonry volume.
The default dry-volume factor is editable.
Do not use a generic ratio where the project specification requires a tested or engineered mortar.
Use this only when the drawing or specification expressly allows a nominal PCC mix.
1 : 2 : 4
Cement : Sand : Coarse aggregate · by volume · example dry factor 1.54
Calculation
Ingredient volume = finished concrete × dry-volume factor × ingredient part ÷ total parts.
Worked example
For 1 m³ finished volume and a 1.54 dry factor, total dry ingredients are 1.54 m³. At 1:2:4, the shares are 0.22 m³ cement, 0.44 m³ sand and 0.88 m³ aggregate before wastage.
Check before using this example
If an approved project document does not allow this nominal mix, enter the constituent quantities from the approved design mix instead.
Ratio parts are by loose volume.
The displayed mix and dry-volume factor are editable planning inputs.
Moisture, batching and compaction adjustments are outside this arithmetic.
No nominal ratio is presented as universally structurally suitable.
The calculator does not design concrete or verify strength, durability or exposure requirements.
Calculate cement and sand for a measured screed or bedding layer when the specification gives a volume ratio.
1 : 4
Cement : Sand · by volume · example dry factor 1.33
Calculation
Wet volume = area × thickness; ingredient volume = wet volume × dry factor × ratio share.
Worked example
For 20 m² at 40 mm, wet volume is 0.8 m³. Apply the project dry-volume factor, then split the result using the specified cement:sand ratio.
Check before using this example
There is no universal screed ratio here. Match the ratio and factor to the product or project specification.
Thickness is averaged across the measured area.
Falls, depressions and substrate variation are reflected in the entered average thickness.
Confirm thickness, reinforcement, bonding and performance requirements with the applicable specification.
03
Use the concrete specification to choose the inputs.
A strength grade such as M20, M25 or M30 does not supply the constituent quantities needed for an estimate. Copy those quantities from the approved mix design or supplier schedule.
M20
20 N/mm² at 28 days
Use an approved design mix. CPWD permits a nominal mix for M20 or lower only when design mix cannot be used and the Engineer-in-Charge permits it.
M25
25 N/mm² at 28 days
Use approved design-mix or supplier quantities per cubic metre; do not infer a fixed volume ratio from the grade.
M30
30 N/mm² at 28 days
Use approved design-mix or supplier quantities per cubic metre; do not infer a fixed volume ratio from the grade.
Convert dimensions before multiplying them. Check whether the source gives an ingredient by volume or by weight, and use the bag size and bulk density actually entered in the calculator.
1 metre = 1,000 millimetres.
1 cubic metre = 1,000 litres.
Cement bags = cement volume × entered bulk density ÷ entered bag weight.
Loose dry-volume factors are contextual inputs, not universal physical constants.
Apply your specified mix to your measurements.
The material calculators let you enter the proportions, factors and quoted prices relevant to your work.