Concrete Bag Calculator — ft, bags, cost comparison
How to use this calculator
Pick a preset for the most common small pours, or enter your own volume. The calculator rounds every bag size up and flags the cheapest option per bag size once prices are entered — the number you see is what to load in the truck, not a theoretical minimum.
Direct volume — enter yd³ or ft³ if you already know the volume.
Dimensions — enter L × W × D in feet and inches.
Waste — 10% for clean formwork, 15% for footings poured against soil.
| Bag Size | Yield | Bags | Weight | Cost |
|---|---|---|---|---|
| 40 lb | 0.30 ft³ | — | — | — |
| 50 lb | 0.375 ft³ | — | — | — |
| 60 lb | 0.45 ft³ | — | — | — |
| 80 lb | 0.60 ft³ | — | — | — |
| 90 lb | 0.675 ft³ | — | — | — |
Saved Calculations
| Time | Volume | 40 lb | 60 lb | 80 lb | Best Cost |
|---|
How Many Bags of Concrete Do I Need?
Bagged concrete (Quikrete, Sakrete, Sika) is economical only for small pours — footings, post bases, slab repairs, and pads up to roughly 1 yd³. Above that, ready-mix delivery is almost always cheaper per yard once you account for mixing labor. This tool compares the 40, 50, 60, 80, and 90 lb sizes so you can see the break-even at a glance.
How to use it
Enter a known volume in yd³ or ft³, or switch to Dimensions and type length × width × depth (feet, inches, and fractions). A 10 ft × 10 ft slab at 4 in is the default. The waste slider adds an allowance for spillage, sub-base irregularity, and partial bags — 10% is typical for flatwork, 15% for footings poured against rough soil.
Bag yield reference (ASTM C387)
40 lb = 0.30 ft³ (0.011 yd³) · 50 lb = 0.375 ft³ (0.014 yd³) · 60 lb = 0.45 ft³ (0.017 yd³) · 80 lb = 0.60 ft³ (0.022 yd³) · 90 lb = 0.675 ft³ (0.025 yd³). Mixed density is about 150 pcf per ACI 318-19, so 27 ft³ of placed concrete weighs roughly 4,000 lb.
Formulas
Volume: Vft³ = Lft × Wft × (Din ÷ 12); divide by 27 for yd³.
Bags: N = ⌈Vft³ × (1 + waste) ÷ yieldbag⌉ (rounded up — you cannot buy a partial bag).
Cost: per size = N × price/bag; the lowest non-zero total is flagged as best value.
Related concrete calculators
For structural pours, size the section first: the concrete beam calculator and concrete column calculator return both volume and rebar. For larger flatwork use the concrete volume calculator, and for vertical work the concrete wall calculator. Site work is covered by the curb & gutter calculator and the concrete stairs calculator.
FAQ
Which bag size is best? 80 lb bags are the most popular for medium projects — best balance of yield and handling weight. Use 40–60 lb bags for small repairs or back-friendly handling, and 90 lb bags for large volumes.
How many 80 lb bags per yard? Approximately 45 bags of 80 lb concrete per cubic yard (27 ft³ ÷ 0.6 ft³ per bag = 45). At ~45 bags/yd³, ready-mix usually wins above 1–2 yd³.
Why round up every bag size? Bags are sold whole, and a short pour cannot be patched cleanly once it sets, so the calculator always ceilings the bag count after applying waste.
Ordering tips
In 2025 USA, 80 lb bags run about $5.50–7.50 (Quikrete/Sakrete standard), 60 lb $4.50–6, and high-early Type III fast-setting bags $7–10. The most common estimator mistake is buying for the dry volume printed on the bag and skipping the waste line — partial bags, spillage, and a slightly over-dug post hole easily add 10–15%. Above roughly 1 yd³ (about 45 of the 80 lb bags), price out ready-mix instead: even with a short-load fee a truck usually wins on $/yd³ and saves a full day of mixing. Per ACI 318-19, bagged mixes labeled 4000 psi at 28 days are fine for residential footings and slabs on grade; use high-strength 5000 psi for driveway aprons, garage slabs, and any pour exposed to freeze-thaw.
