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.
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.
Adjust water slowly on-site for moisture, slump, temperature, and mixer performance.
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.Waste volume = wet volume × waste percentage.Dry volume = (wet volume + waste volume) × dry-volume factor.Total ratio parts = cement parts + sand parts + aggregate parts.Component volume = dry volume × component parts ÷ total parts.Component weight = component volume × density.Cement bags = cement weight ÷ bag size, rounded up for buying.Water estimate = cement weight × water-cement ratio, shown as liters and gallons.Mixer batches = (wet volume + waste volume) ÷ mixer capacity, rounded up.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. |
| M25 | 1:1:2 | 25 MPa / 3,625 psi | Higher-strength slabs and reinforced members | Usually should be design-controlled | More cement-rich and less forgiving by eye. |
| M30 | 1:0.75:1.5 | 30 MPa / 4,350 psi | Engineered concrete applications | Do not use as a casual site recipe | Use a tested mix design and batching controls. |
| General | 1:2:3 | Varies by materials | Small mixer pours, paths, utility pads | Not a grade specification | Popular bucket ratio for practical mixing. |
Inputs: 1 m³, M15, dry factor 1.54, waste 5%, 50 kg bags, w/c 0.50.
Estimate: about 333 kg cement, 6.7 bags, 0.46 m³ sand, 0.92 m³ aggregate, and 166 L starting water.
Buying takeaway: plan for 7 bags of cement plus rounded-up sand and aggregate deliveries.
Inputs: 1 yd³, 1:2:3, dry factor 1.54, waste 5%, 94 lb bags.
Estimate: about 654 lb cement, 7.0 bags, 14.6 ft³ sand, 21.8 ft³ aggregate, and 39 gal starting water.
Buying takeaway: round to 7 or 8 bags depending on handling loss and subgrade tolerance.
Inputs: dimensions mode, M20 1:1.5:3, dry factor 1.54, waste 5%.
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.
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.
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.
Use the same bucket for every part. For 1:2:4, each cement bucket gets 2 buckets of sand and 4 buckets of aggregate.
Keep some water back until the mix rolls cleanly and coats the aggregate. Extra water weakens concrete and increases shrinkage.
Flatwork usually needs a cohesive, plastic mix that can be placed without becoming soupy. If it slumps flat immediately, it is probably too wet.
Damp sand adds hidden water and can bulk up by volume. Reduce starting water and keep batch measurements consistent.
Large slabs, driveways, structural pours, hot weather, and tight finishing windows often justify ready-mix for consistency and speed.
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.
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.
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.
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.
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.
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.
Wet sand contributes water to the mix, so start with less added water and increase gradually until the slump is workable.
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.
Enter the bag size in Advanced settings. The calculator divides estimated cement weight by that bag size and rounds up for purchase planning.