Mixing Calculator 2026

For C20/25 concrete (standard), the mixing ratio is 1:3:5 (cement : sand : gravel). Per cubic meter, approximately 300 kg cement, 640 kg sand (0-4mm) and 1,180 kg gravel (4-16mm) are needed. The water-cement ratio is 0.55, meaning about 165 liters of water per cubic meter.

Cement requirements depend on the concrete class: C12/15 (lean concrete) needs approx. 250 kg/m3, C20/25 (standard) approx. 300 kg/m3, C25/30 (foundation) approx. 350 kg/m3 and C30/37 (heavy-duty) approx. 400 kg/m3. That is 10 to 16 bags of cement (25 kg) per cubic meter.

The epoxy mixing ratio depends on the product. Common ratios are 2:1 (standard, by volume), 3:1 (slow curing), 5:1 (coatings) and 100:45 (by weight, EU standard). The exact ratio is always printed on the manufacturer packaging. Deviations lead to poor curing.

Deep primer is diluted based on the surface: Apply undiluted on normally absorbent surfaces (coverage approx. 6 sqm/L). On highly absorbent surfaces, first apply diluted 1:1 with water, then roll undiluted. Use undiluted on drywall (approx. 7 sqm/L).

Consumption depends on the trowel notch: 6mm notch approx. 2.5 kg/sqm, 8mm approx. 3.5 kg/sqm, 10mm approx. 4.5 kg/sqm, 12mm approx. 5.5 kg/sqm. For large format tiles (>60cm) using buttering-floating method, add approx. 50%. A 25 kg bag covers approx. 5-7 sqm with 8mm notch.

The formula is: kg/sqm = (tile length + tile width) / (length x width) x joint width x tile thickness x density. Example: 60x60cm tile, 3mm joint, 10mm thick: (0.6+0.6)/(0.6x0.6) x 0.003 x 0.01 x 1600 = 0.27 kg/sqm. For 15 sqm, approx. 4 kg of grout is needed.

Minimum thickness is usually 1-3mm, maximum per layer is 10mm. For leveling above 10mm, work in multiple layers. Consumption is approx. 1.5 kg/sqm per mm of thickness. With underfloor heating, plan at least 45mm of coverage.

Pot life (working time) for most epoxy resins is between 20 and 45 minutes. Coatings and crack injections have approx. 25 minutes, casting resins approx. 45 minutes. After pot life expires, the mixture becomes viscous and unworkable. Larger quantities increase temperature and shorten pot life.

Gypsum filler: Interiors, joints, holes (4h drying). Cement filler: Exterior and wet rooms (24h). Fine filler: Finishing before painting (2h). Repair filler: Quick hole filling (1h). 2K filler: Wood and metal, extremely hard (30 min).

For 1 cubic meter of concrete, approximately 67 bags of premix concrete (40 kg each) are needed (one 40 kg bag yields approx. 0.015 m3). That equals about 2,680 kg total weight. By comparison: self-mixing with cement, sand and gravel costs about half, but requires more effort and a concrete mixer.