Concrete Mix Ratio Calculator – 1:2:4 & M20

Instead of working from a supplier's ballpark figure, this calculator derives your concrete mix requirement from Dry Volume = Wet Volume × 1.52; Cement = (Ratio ÷ Sum) × 1.52 ÷ 0.035 using the exact wet volume and mix ratio you provide. The arithmetic stays transparent: each result links back to the displayed formula, so you can audit any number. For instance: For 1 m³ of 1:2:4: cement 6.34 bags, sand 0.44 m³, gravel 0.88 m³ (dry factor 1.52 applied). Keep in mind: M20 ≈ 1:1.5:3 - about 8 bags of cement per m³. Quantities are rounded conservatively so offcuts, spillage and delivery shortages never stop work mid-job.

1. 1

   Measure the space

   Record the wet volume and mix ratio at the widest and longest points.

2. 2

   Enter the values

   Type the measurements into the calculator and select your units.

3. 3

   Apply the formula

   The tool computes Dry Volume = Wet Volume × 1.52; Cement = (Ratio ÷ Sum) × 1.52 ÷ 0.035 for your inputs instantly.

4. 4

   Add waste and order

   Review the total with a 5-10% margin and round up to whole units.

• Measuring in mixed units

• Forgetting the waste factor

• Ordering exact volume