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Concrete Mix Calculator: On-Site Batch & Ready-Mix Order

By Nick Major · Founder, Calculator Campus Last updated June 30, 2026

This concrete mix calculator turns your pour shape, dimensions, mix grade, bag size, and waste allowance into a practical concrete order. Start with on-site batch mode to see cement, sand, aggregate, water, and whole cement bags. Switch to ready-mix order when you need cubic yards and cubic meters for a supplier. The tool covers slabs, walls, columns, tubes or ring footings, strip footings, and simple stair rectangles.

Start in on-site batch mode for cement, sand, aggregate, water, and bag counts. Switch to ready-mix order when you only need cubic yards for a supplier; the same shape and waste inputs are reused.

Primary output 10 cement bags
Choose on-site batch for raw material quantities, or ready-mix order for cubic yards to request from a supplier.
Pick the geometry that matches your forms.
Imperial uses feet for length/height and inches for thickness/diameter. Metric uses meters for length/height and millimeters for thickness/diameter.
Length in feet or meters for slabs, walls, strip footings, and stair rectangle estimates.
Width in feet or meters for slabs and strip footings.
Use inches in imperial mode or millimeters in metric mode. For walls, this is wall thickness.
Height in feet or meters for walls, columns, and tubes.
Use inches in imperial mode or millimeters in metric mode.
Tube or ring pours only. Must be smaller than the outer diameter.
Use this for repeated footings, columns, or matching slabs.
Selects the nominal cement:sand:aggregate parts and water/cement ratio used for material quantities.
Advanced options
Net volume 0.94 m³ Water/cement 0.55 Notes —
Used to round cement mass up to whole bags for on-site batching.
Adds extra volume for spills, uneven subgrade, and ordering cushion.
Used only when Mix grade is Custom.
Used only when Mix grade is Custom.
Used only when Mix grade is Custom.
Used only when Mix grade is Custom.
Answer 10 cement bags
Cement bags 10 bags
Cement 418.6 kg
Sand 697.7 kg
Aggregate 1,264.6 kg
Water 230.2 L
Order volume (m³) 1.04 m³
Net volume (m³) 0.94 m³
Water/cement ratio 0.55
Show calculation details
Net volume (ft³) 33.33 ft³
Mix ratio 1:1.5:3
Nominal class C20
Dry-volume basis 1.6 m³
Notes —

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How to check the math

Rectangular pour volume

Multiply form length by width and slab thickness. Scale by element count to find total wet volume.

Volume = Length × Width × Thickness × Quantity
Circular column volume

Square the column radius, multiply by pi and height, then scale by column count to get total wet volume.

Volume = π × (Diameter / 2)² × Height × Quantity
Tube or hollow circular slab volume

Subtract the bore area from the outer circle area, then multiply by height, pi, and element count.

Volume = π × ((Outer Diameter / 2)² − (Inner Diameter / 2)²) × Height × Quantity
Order volume with waste

Increase wet volume by the waste percent to cover spills and overrun before placing the order.

Ordered Volume = Volume × (1 + Waste Percent / 100)
Cubic yards conversion

Divide ordered volume in cubic meters by 0.764554858 to convert to cubic yards for US concrete orders.

Cubic Yards = Ordered Volume / 0.764554858
Dry volume uplift

Multiply ordered volume by 1.54 to account for voids in dry materials that close when water is added.

Dry Volume = Ordered Volume × 1.54
Material masses from a nominal mix

Multiply each material's dry-volume share by its bulk density. The share comes from dividing that material's mix part by total parts.

Material Mass = Dry Volume × (Mix Part / Total Parts) × Bulk Density
Water cement ratio

Multiply the water-cement ratio by cement mass to find the water needed, following ACI 318-19 guidelines.

Water Mass = Water-Cement Ratio × Cement Mass
Cement bag count

Divide cement mass by the standard bag weight, then round up to purchase only whole bags.

Cement Bags = Ceiling(Cement Mass / Bag Size)
Methodology

How the answer is computed

The calculator finds wet concrete volume from the selected shape, applies the waste percentage, and then converts the order volume to cubic yards using 1 yd³ = 0.764554858 m³. In on-site batch mode it multiplies the order volume by the 1.54 dry-volume factor, splits that dry volume by the selected cement:sand:aggregate ratio, applies loose bulk densities, computes water from the selected water/cement ratio, and rounds cement up to whole bags.

Worked examples

See the math step by step

Residential garage floor slab

Maria needs to pour a concrete floor for her one-car garage in Denver before October frost arrives. The slab is 12 feet long, 10 feet wide, and 4 inches thick — standard for a residential garage floor. Converting to metric gives 3.6576 meters long, 3.048 meters wide, and 0.1016 meters deep.

The wet volume is 3.6576 × 3.048 × 0.1016 = 1.1326 cubic meters. Adding 10 percent for waste gives an ordered volume of 1.1326 × 1.10 = 1.25 cubic meters. One cubic yard holds 0.7646 cubic meters, so 1.25 ÷ 0.7646 = 1.63 cubic yards. Ready-mix suppliers sell in quarter-yard increments, so Maria rounds up and orders 1.75 cubic yards on her delivery ticket.

Garden shed concrete floor

Jen is building a small storage shed in her backyard and needs to pour a concrete floor first. The slab is 10 feet long, 8 feet wide, and 4 inches thick. In metric, those dimensions are 3.048 meters × 2.4384 meters × 0.1016 meters.

The wet volume works out to 3.048 × 2.4384 × 0.1016 = 0.75 cubic meters. Adding a 10 percent waste buffer brings the order to 0.75 × 1.10 = 0.83 cubic meters. One cubic yard equals 0.7646 cubic meters, so 0.83 ÷ 0.7646 = 1.09 cubic yards. Jen's supplier sells in half-yard increments, so she orders 1.5 cubic yards and has a little left for a small step near the door.

When to use this calculator

Use this tool when you know the dimensions of a concrete form and need either a raw-material batch list or a ready-mix order volume. For a slab or footing, enter length, width, and thickness. For a wall, enter length, wall thickness, and height. For round columns or tubes, enter the diameter and height; tube mode subtracts the inner bore.

Why waste is applied before the order conversion

Concrete shortages are expensive because a second truck or a late hand batch can create a cold joint. The calculator applies your waste percentage to the wet volume first, then converts that larger value to cubic yards or dry-material quantities so the contingency follows the whole estimate.

What the mix-grade preset changes

Changing from C20 to C25 does more than rename the result. The preset changes the cement:sand:aggregate parts and the water/cement ratio used for the material breakdown. That is why the same slab can need a different cement mass and water quantity when you pick a stronger nominal mix.

Assumptions

What we assume

  • Waste is applied to wet volume before cubic-yard conversion and before on-site material quantities are calculated.
  • On-site batch quantities use a 1.54 dry-volume factor and loose bulk densities of 1440 kg/m³ cement, 1600 kg/m³ sand, and 1450 kg/m³ aggregate.
  • Preset mix grades are nominal planning ratios; actual strength depends on materials, curing, air, admixtures, batching accuracy, and exposure requirements.
Limitations

What this skips

  • Does not design slab thickness, footing depth, reinforcement, joints, or exposure class.
  • Does not dose admixtures, air entrainment, fibers, accelerators, retarders, or plasticizers.
  • Does not include pump-line losses, truck minimums, short-load fees, or supplier-specific order rounding.
  • Custom mix ratios return material quantities only and do not imply a verified strength class.
Common mistakes

What people miss

  • Mixing feet and inches for the same dimension throws off slab depth by a large margin.
  • You enter a depth of 3 inches when the spec calls for 4, and the pour falls short.
  • Forgetting to add a waste factor means the calculator orders less concrete than the job needs.
  • Rounding the bag count down instead of up leaves you one or two bags short at the finish.
References

References

  1. Ready Mix Concrete Calculator

    CEMEX USA · accessed 2026-06-30

  2. Guide to the SI

    National Institute of Standards and Technology · accessed 2026-06-30

  3. ACI CODE-318-19(22): Building Code Requirements for Structural Concrete

    American Concrete Institute · accessed 2026-06-30

  4. Concrete Mix on Site

    Source4me · accessed 2026-06-30

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