Find out exactly how many bags of concrete you need. Enter your slab dimensions and bag size — get bag count, total weight, and cost instantly.
Calculate concrete volume from length × width × depth, with slab depth presets
Covers spillage, uneven sub-base, and over-dig
A 25kg bag of concrete yields approximately 0.0125m³. A 40kg bag yields about 0.02m³. Always check the manufacturer's yield on the packaging — it varies by mix design and aggregate size.
For bagged concrete, use approximately 2.5-3 litres of clean water per 25kg bag. Too much water weakens the mix. Mix until the consistency is like thick peanut butter — workable but not runny.
Use bagged concrete for jobs under 1m³ (small pads, post holes, repairs). For anything over 2m³, ready-mix delivery is almost always cheaper, faster, and more consistent.
Store bags off the ground on pallets, covered with waterproof sheeting. Concrete absorbs moisture from the air and will set in the bag if left exposed. Use within 6 months of purchase.
V = length × width × depth
bags = ceil(V × (1 + waste%) / yield_per_bag)
weight = bags × bag_weight
cost = bags × price_per_bag
For structural concrete (foundations, retaining walls, structural slabs), consult a structural engineer. Bagged concrete is suitable for non-structural applications like shed bases, patios, and post holes. For load-bearing applications, use ready-mix with a specified mix design.
You need approximately 80 bags of 25kg concrete for 1m³. With 5% waste allowance, order 84 bags. Each 25kg bag yields about 0.0125m³.
Approximately 50 bags of 40kg concrete make 1m³. Each 40kg bag yields about 0.02m³. With 5% waste, order 53 bags.
In the UK, a 25kg bag of general-purpose concrete costs £4-6. In the US, an 80lb (36kg) bag costs $4-7. Bulk discounts apply for orders over 50 bags.
Yes — enter the post hole diameter as width, depth as depth, and a small length. For a 300mm diameter hole at 600mm deep, use width=0.3, length=0.3, depth=0.6.