Bag yields never change — pours always do
One 80-lb bag of bagged concrete mix yields about 0.6 cubic feet, a 60-lb bag 0.45, and a 40-lb bag 0.30 — so a 10×10 slab at 4 inches takes 33⅓ cu ft, or 56 of the 80-lb bags. The calculator turns your pour into all three counts so you can price whichever format your supplier stocks.
Mixing water, roughly
Plan on about 6 pints of water per 80-lb bag, 4 per 60-lb and 3 per 40-lb. Hold back a splash and add it as you mix — a stiffer mix cures stronger, and soupy mix trades strength for workability. In heat above 80°F, use cold water and mix smaller batches.
When to stop buying bags
Past roughly one cubic yard — about 45 of the 80-lb bags — bagged mix loses to a ready-mix truck on both price and your back. Forty-five bags is two-plus hours of mixing for two people and the pour starts curing before the last batch lands. Bagged mix owns the small world: post holes, sidewalk patches, AC pads, grill foundations.
Sources and standards
Where these figures come from
Every formula on this page is implemented from the published reference material below. Where a value depends on a regional code, the calculator lets you override it rather than assuming one jurisdiction.
- ASTM International — C94 for ready-mixed concrete, C150 for cement and C143 for slump testing.
- American Concrete Institute — ACI 318 code requirements and ACI 302 slab construction guidance.
- Portland Cement Association — mix design, yield and curing data published by the US cement industry.
Figures, formulas and reference tables last verified: 19 September 2026.