Work out how much concrete you need for a slab, footing, column or post-hole — plus how many 25 kg ready-mix bags, or how much cement, sand and gravel to buy loose.
One 25 kg dry ready-mix bag yields ~0.012 m³ of set concrete. Loose ratios assume dry weights; add ~10 % for spillage and compaction.
About 85 bags of dry ready-mix (each ~0.012 m³ set). For a 10 × 10 × 0.1 m slab (1 m³) buy ~90 bags to allow for a 5–10 % over-order.
A general 1:2:3 mix (cement : sand : gravel by volume) with ~0.5 water/cement ratio gives ~C20/25. For a footing use a leaner 1:3:6; for a path 1:2:4.
Roughly 2.5–3 L per 25 kg bag. Add in stages until the mix balls in your gloved hand without slumping — too much water halves the final strength.
For anything over 80 mm thick or that will carry a car, add A142 mesh mid-depth. Thin paths under 60 mm can go without, but expect hairline shrinkage cracks.
Estimates only. Check the paint tin / adhesive bag for the exact coverage of your product.