Calculate cement, sand, aggregate, water, cement bags, dry volume, and mixer batches for slabs, footings, driveways, paths, pads, post holes, and small cement mixer pours.
Project Details
Use the finished concrete volume before dry-volume adjustment.
Post-hole preset uses a square allowance. Increase waste or volume for round holes, bell bottoms, or rough excavation.
Ratios are volume parts. Strengths are approximate 28-day planning labels, not approved mix designs.
Batch counts use wet yield including waste. Keep actual loads below the rated drum size if your mixer struggles.
Advanced assumptions
Common planning range: about 1.50 to 1.57.
Covers spillage, uneven subgrade, and rounding up.
Start around 0.45 to 0.55 for many site mixes, then adjust for slump.
Use 25 kg, 50 kg, 80 lb, 94 lb, or your local bag size.
Loose Portland cement is often estimated near 1440 kg/m³.
Wet or compacted sand can be heavier than dry loose sand.
Crushed stone and gravel vary by source and grading.
Cement type affects setting and strength gain; this quantity estimate still uses your density and ratio inputs.
Material Estimate
Wet concrete volume:-
Waste allowance:-
Dry material volume:-
Total ratio parts:-
Cement volume:-
Cement weight:-
Cement bags:-
Sand volume:-
Sand weight:-
Aggregate volume:-
Aggregate weight:-
Starting water:-
Mixer batches:-
Per-batch guide
Cement per batch:-
Sand per batch:-
Aggregate per batch:-
Starting water per batch:-
Adjust water slowly on-site for moisture, slump, temperature, and mixer performance.
How to use this concrete mix calculator
Enter a known wet concrete volume, or switch to length × width × depth for slabs, pads, paths, footings, and post-hole allowances.
Pick a grade preset such as M15 1:2:4 or M20 1:1.5:3, or enter your own cement:sand:aggregate volume parts.
Adjust the dry-volume factor, waste, water-cement ratio, cement bag size, densities, and cement type note when your local materials differ.
Use mixer batch mode to split the total into cement bags or buckets, sand buckets, aggregate buckets, and starting water per batch.
How this is calculated
Concrete ratios are volume parts: a 1:2:4 mix means 1 part cement, 2 parts sand, and 4 parts coarse aggregate. Dry ingredients contain voids and compact after water is added, so estimating dry material volume is higher than the finished wet concrete volume.
Wet volume = known volume, or length × width × depth converted to cubic meters.
These nominal ratios are planning estimates. Structural concrete, reinforced concrete, suspended slabs, and code-controlled work should follow project drawings, local code, exposure requirements, and an approved engineered mix design.
Grade
Mix ratio
Approx. 28-day strength
Best uses
Limitations
Notes
M5
1:5:10
5 MPa / 725 psi
Lean fill, bedding
Not for slabs or structural work
Very low cement content.
M7.5
1:4:8
7.5 MPa / 1,090 psi
Blinding, sub-base layers
Low strength
Useful under footings before main concrete.
M10
1:3:6
10 MPa / 1,450 psi
Leveling courses, light non-structural work
Limited durability under traffic
Common lean concrete planning ratio.
M15
1:2:4
15 MPa / 2,175 psi
Paths, patios, small slabs, light pads
Check suitability for driveways and reinforcement
Common all-purpose site mix.
M20
1:1.5:3
20 MPa / 2,900 psi
Driveways, reinforced slabs, footings
Still needs engineering where structural
Often selected when a stronger nominal mix is needed.
Estimate: wet volume is 1.48 yd³ before waste; about 1,057 lb cement, 11.3 bags at 94 lb, 17.6 ft³ sand, 35.3 ft³ aggregate, and 63 gal starting water.
Buying takeaway: a small mixer will need many batches, so compare labor against ready-mix delivery.
Fence-post or small footing allowance
Inputs: 1 ft × 1 ft × 3 ft allowance, M15 1:2:4, dry factor 1.54, waste 10% for rough digging.
Estimate: about 30 kg cement, 0.6 of a 50 kg bag, 0.04 m³ sand, 0.08 m³ aggregate, and 15 L starting water.
Buying takeaway: round up by whole bags and reuse leftover dry aggregate on the next hole.
Practical site-mixing guide
Load the mixer consistently
Start with part of the water, add coarse aggregate, then sand and cement. Add the remaining water gradually so dry cement does not cake on the drum.
Measure by bucket
Use the same bucket for every part. For 1:2:4, each cement bucket gets 2 buckets of sand and 4 buckets of aggregate.
Add water gradually
Keep some water back until the mix rolls cleanly and coats the aggregate. Extra water weakens concrete and increases shrinkage.
Check slump by eye
Flatwork usually needs a cohesive, plastic mix that can be placed without becoming soupy. If it slumps flat immediately, it is probably too wet.
Account for wet sand
Damp sand adds hidden water and can bulk up by volume. Reduce starting water and keep batch measurements consistent.
Know when to order ready-mix
Large slabs, driveways, structural pours, hot weather, and tight finishing windows often justify ready-mix for consistency and speed.
Methodology and sources
Editorial methodology, last updated June 9, 2026: this calculator uses nominal volume ratios for planning quantities, not approved structural mix designs. Defaults are 1.54 dry-volume factor, 5% waste, 0.50 water-cement ratio, 1440 kg/m³ cement density, 1600 kg/m³ sand density, and 1500 kg/m³ aggregate density. You can adjust each assumption above.
Dry-volume factors commonly fall around 1.50 to 1.57 because dry materials have voids and consolidate after mixing. Water-cement ratio is shown as a starting estimate only; aggregate moisture, grading, admixtures, placement, and curing all affect actual water demand and strength.
A 1:2:4 ratio means 1 volume part cement, 2 volume parts sand, and 4 volume parts coarse aggregate before water is added.
Which concrete mix ratio is best for slabs?
Many non-structural slabs use M15 1:2:4 or M20 1:1.5:3 as planning ratios, but driveways, reinforced slabs, and structural work should follow drawings, local code, and engineered mix designs.
How much cement is needed for 1 m3 of concrete?
For M15 1:2:4 with a 1.54 dry-volume factor and 5% waste, the calculator estimates about 333 kg of cement, or roughly 6.7 bags at 50 kg each.
Why is dry volume higher than wet concrete volume?
Dry ingredients have voids and compact after mixing with water. Estimators often multiply wet volume by a dry-volume factor such as 1.50 to 1.57 before splitting cement, sand, and aggregate.
How does water-cement ratio affect concrete strength?
Lower water-cement ratios usually increase paste strength but make concrete harder to place. Extra water improves workability but can reduce strength and increase shrinkage.
Can this calculator be used for RCC or structural concrete?
Use it only for planning quantities. Reinforced or structural concrete should be proportioned from project drawings, local code, exposure requirements, and an approved mix design.
How does wet sand change the water estimate?
Wet sand contributes water to the mix, so start with less added water and increase gradually until the slump is workable.
Does this work for ready-mix concrete?
For ready-mix, use the wet concrete volume and waste allowance as an order estimate. Ready-mix suppliers proportion materials by their own approved batch designs.
How many 25 kg, 50 kg, 80 lb, or 94 lb cement bags are needed?
Enter the bag size in Advanced settings. The calculator divides estimated cement weight by that bag size and rounds up for purchase planning.
