Concrete Calculators
Work out how much concrete to order for a slab, patio, shed base or post holes — in cubic yards, cubic metres and bags — before you head to the store or call the ready-mix plant.
Where to start?
- Pouring a slab, patio or shed base → Concrete Slab Calculator
- Small job, setting posts or a repair — buying bags → Concrete Bag Calculator
All concrete calculators
- Concrete Slab Calculator Estimate cubic yards, cubic metres and bags of concrete for a slab, patio or pad — with waste factor, the formula and a shopping list.
- Concrete Bag Calculator How many bags of concrete do you need? Compare 40, 60 and 80 lb or 20, 25 and 30 kg bags, total weight and cost — with the math shown.
Coming soon: Footing / Sonotube · Concrete steps · Rebar grid
How concrete estimating works
Concrete is sold by volume, but it is bought in two very different ways. Ready-mix trucks deliver by the cubic yard (US) or cubic metre (UK, Australia, Canada), usually with a minimum load and a short-load fee. Bagged premix is sold by weight — 40, 60 and 80 lb in the US, 20, 25 or 30 kg elsewhere — and each bag yields a fixed volume printed on the label. Our calculators work out the volume first, then translate it into the unit you will actually buy.
The two questions that change the answer most are thickness and waste. Thickness is entered in inches or centimetres while length and width are in feet or metres, and mixing those up is the classic mistake. Waste covers spillage, a sub-base that is not perfectly flat, and forms that bow slightly under load; 5–10% is typical for a prepared base.
For anything structural — footings for an extension, suspended slabs or retaining walls — use these numbers for budgeting only and follow local code or an engineer's design.
Glossary
- Ready-mix
- concrete batched at a plant and delivered by truck
- Premix / bagged concrete
- dry cement, sand and aggregate in a bag; add water on site
- Postcrete (UK)
- fast-setting post-fixing mix
- Sub-base / hardcore
- compacted stone layer under a slab
Updated by the DIYCalcLab Editorial Team · How we calculate
Guides
- How Much Concrete Do I Need? A Step-by-Step GuideWork out concrete volume for slabs, footings and post holes in cubic yards, cubic metres and bags — with worked examples, waste allowances and ordering tips.
- Bagged Concrete vs Ready-Mix: Which Should You Use?When to mix bags yourself and when to order a ready-mix truck — volume thresholds, labour, finish quality and the questions to ask a supplier.
- How to Plan a Deck: Size, Layout and MaterialsPlan a deck from site to materials list: choosing size around board lengths, board direction, gaps, joist spacing, footings and the permits you may need.
- Fence Planning Checklist: Before You Dig the First HoleA practical checklist for planning a wood or panel fence: boundaries, permits, layout, post spacing, gates, materials and concrete per post.
Other categories
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