How to use this calculator
- Enter Length in ft.
- Enter Width in ft.
- Enter Thickness in in.
- Enter Bag size.
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
Bag yields: 80 lb = 0.60 cu ft, 60 lb = 0.45, 50 lb = 0.375, 40 lb = 0.30. Divide pour volume in cubic feet by yield and round up. Bags suit pours under about one cubic yard. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.
Where this fits in the project
Concrete work starts below grade: excavation, then a compacted gravel base for drainage, formwork, rebar where the slab spec requires it, then the pour. Order by cubic yard and round up — a short load fee costs more than surplus material.
How this connects to your project
No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the concrete bag calculator:
- Concrete Calculator — Bag calculator is for small projects vs bulk concrete.
- Concrete Slab Calculator — Small slabs are often done with bagged concrete.
- Concrete Footing Calculator — Deck footings commonly use bagged concrete.
- Concrete Cost Calculator — Compare bagged vs ready mix costs.
- Fence Post Depth Calculator — Fence posts are set in bagged concrete.
- Deck Calculator — Deck footings use bagged concrete.
- Retaining Wall Calculator — Some retaining walls need concrete footings.
Frequently asked questions
How many bags for a 10×10 slab at 4 in?
33.3 cu ft → 56 bags of 80 lb mix with 5% waste. At that count, price ready-mix delivery too.
How much water per 80 lb bag?
About 3 quarts. Excess water is the #1 DIY strength killer — wetter is weaker.
Last verified: — prices reflect current national averages. See our methodology.
Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.