Concrete Mix Design Calculator
Estimate the total cement mass needed for a concrete batch based on target strength, volume, exposure conditions, and aggregate size. Use it when planning material quantities for slabs, columns, or footings.
Last updated: September 2026
Formula below · 2 sources (asce.org, Wikipedia) · Updated Sep 2026
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About this calculator
This calculator estimates the cement needed using the ACI 211.1 absolute-volume method for normal-weight, non-air-entrained concrete. Step 1 — mixing water from the maximum aggregate size (ACI 211.1 Table 6.3.3, 75–100 mm slump): about 205 kg/m³ for 20 mm, 193 kg/m³ for 25 mm and 181 kg/m³ for 40 mm aggregate. Step 2 — water-cement ratio from the target strength (ACI 211.1 Table 6.3.4(a)): 0.79 at 15 MPa, 0.69 at 20, 0.61 at 25, 0.54 at 30, 0.47 at 35 and 0.42 at 40 MPa, interpolated between. Step 3 — the exposure limit: the lower of the strength-based ratio and the exposure maximum (0.45 severe, 0.50 moderate, 0.55 mild) is used. Step 4 — Cement (kg) = volume × water ÷ (w/c). Enter the target average strength f′cr that the mix must achieve, not the specified strength f′c: without test history ACI 318 requires f′cr = f′c + 8.3 MPa for 21–35 MPa concrete. Admixtures, air entrainment and supplementary materials change these figures, so verify the final mix by trial batches (ACI 211.1).
How to use
Goal: cement for 5 m³ of concrete with a target average strength of 32 MPa, moderate exposure (maximum w/c 0.50) and 20 mm aggregate. Step 1: Water for 20 mm aggregate = 205 kg/m³. Step 2: Strength-based w/c at 32 MPa, between 0.54 (30 MPa) and 0.47 (35 MPa): 0.54 − 0.07 × 2/5 = 0.512. Step 3: Exposure limit 0.50 is lower, so w/c = 0.50. Step 4: Cement = 5 × 205 / 0.50 = 2,050 kg (410 kg/m³). The defaults (10 m³, 25 MPa, moderate exposure, 20 mm) give w/c = min(0.61, 0.50) = 0.50 and 4,100 kg of cement. Sand and coarse aggregate are then proportioned by absolute volume.
Frequently asked questions
What is the standard water-cement ratio for 25 MPa concrete mix design?
In ACI 211.1 Table 6.3.4(a), a non-air-entrained mix with a required average strength of 25 MPa uses a water-cement ratio of about 0.61, and 30 MPa about 0.54. Because the required average strength must exceed the specified strength (by 8.3 MPa for 21–35 MPa concrete when there is no test record), a specified 25 MPa concrete is usually designed near 33 MPa, a w/c ratio of about 0.50. For reinforced concrete in moderate to severe exposure, ACI 318 caps the w/c ratio at 0.45 to 0.40 regardless of strength. Lower ratios need plasticizers to keep workability.
How does maximum aggregate size affect concrete mix proportions?
Larger aggregate sizes reduce the total surface area that cement paste must coat, decreasing the cement and water needed for a given strength and workability. For example, switching from 10 mm to 40 mm aggregate can cut water demand by 20–30 kg/m³. However, aggregate size is limited by the narrowest reinforcement spacing, cover depth, and member thickness — typically no more than one-third of the slab depth or three-quarters of the minimum clear spacing between bars. Optimal aggregate size balances economy with constructability.
Why does exposure condition change the cement content in concrete mix design?
Exposure conditions such as freeze-thaw cycles, sulfate attack, chloride ingress, or abrasion demand a denser, less permeable concrete microstructure. Achieving lower permeability requires reducing the water-cement ratio, which in turn means more cement for the same workability. ACI 318 and EN 206 define exposure classes (XC, XS, XF, etc.) with maximum w/c ratios and minimum cement contents for each class. Ignoring exposure when designing a mix can lead to premature deterioration, spalling, or corrosion of reinforcement, significantly increasing lifecycle costs.