Ratios need context
Use these editable references to follow the arithmetic, then check the actual value against the project specification. There is no single mix for every job.
M20, M25 and M30 are strength grades, not universal mix ratios. The calculators therefore scale approved design-mix quantities instead of inventing cement, sand or aggregate proportions.
M20 states characteristic compressive strength at 28 days; it is not one fixed cement:sand:aggregate ratio. Enter the approved per-m³ design-mix quantities, or price the measured ready-mix volume.
CPWD concrete specification20 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 states characteristic compressive strength at 28 days; it is not one fixed cement:sand:aggregate ratio. Enter the approved per-m³ design-mix quantities, or price the measured ready-mix volume.
CPWD concrete specification25 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 states characteristic compressive strength at 28 days; it is not one fixed cement:sand:aggregate ratio. Enter the approved per-m³ design-mix quantities, or price the measured ready-mix volume.
CPWD concrete specification30 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.
Use this after subtracting the solid bricks from the masonry volume to find the wet mortar between them.
Formula
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.
• 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.
The displayed ratio is only a starting point. Check it against the project specification, brick type and site practice.
• Do not use a generic ratio where the project specification requires a tested or engineered mortar.
Turn a measured surface area and average plaster thickness into cement and plaster sand.
Formula
Wet volume = area × thickness; ingredient volume = wet volume × dry factor × ingredient part ÷ total parts.
Worked example
For 10 m² at 12 mm, wet volume is 0.12 m³. A 1.33 factor gives 0.1596 m³ dry ingredients; at 1:4, cement is 0.0319 m³ and sand is 0.1277 m³.
• Surface area is net of openings or other deductions.
• Thickness is uniform for the worked quantity.
• The dry-volume factor and ratio remain editable.
Check the finish specification, substrate and product instructions. An uneven background can use much more material.
• This ratio is a quantity-planning aid, not a performance specification.
Use this only when the drawing or specification expressly allows a nominal PCC mix.
Formula
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.
• 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.
If an approved project document does not allow this nominal mix, enter the constituent quantities from the approved design mix instead.
• No nominal ratio is presented as universally structurally suitable.
• The calculator does not design concrete or verify strength, durability or exposure requirements.
Scale the constituent quantities already given in an approved mix design or project specification.
Formula
Constituent quantity = finished concrete volume × approved constituent quantity per cubic metre.
Worked example
If the approved schedule states 340 kg cement per m³, then 2.5 m³ requires 850 kg before the entered wastage allowance.
• All per-m³ quantities are copied from the applicable approved design or supplier data.
• Units are checked before entry.
Keep the mix-design or specification reference with the project record.
• The tool scales user inputs only; it neither creates nor approves a mix design.
Calculate cement and sand for a measured screed or bedding layer when the specification gives a volume ratio.
Formula
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.
• Thickness is averaged across the measured area.
• Falls, depressions and substrate variation are reflected in the entered average thickness.
There is no universal screed ratio here. Match the ratio and factor to the product or project specification.
• Confirm thickness, reinforcement, bonding and performance requirements with the applicable specification.