Primary material
62 bags
80 lb concrete mix
Use the calculated bag count as your buying starting point, then verify yield and pallet limits with the store.
Concrete hub
Concrete calculator for yards, bags, and cost.
Start with the slab calculator, then use the same estimating pattern for post holes, footings, walls, columns, stairs, curbs, and cost planning.
Quick reference
Concrete per 100 square feet by thickness
Cubic yards and bags for every 100 sq ft of slab, including the default 10% waste. Multiply by your area divided by 100.
| Thickness | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 3 in thick | 1.02 yd³ | 46 | 62 |
| 4 in thick | 1.36 yd³ | 62 | 82 |
| 5 in thick | 1.70 yd³ | 77 | 102 |
| 6 in thick | 2.04 yd³ | 92 | 123 |
| 8 in thick | 2.72 yd³ | 123 | 163 |
Volume is length x width x thickness, all in feet, divided by 27 for cubic yards.
Concrete tools
Pick the shape before you buy material
Different concrete shapes need different formulas. The hub keeps the shape decision close to the calculator.
Concrete slab Length, width, thickness, yards, bags, and material cost. Live Post hole concrete Hole count, diameter, depth, and 40/60/80 lb bags. Live Concrete footing Continuous or pad footings with yards and bags. Live Concrete wall Wall length, height, thickness, yards, and ready-mix cost. Live Concrete column Round column diameter, height, yards, and bags. Live Concrete stairs Rise, run, width, step count, and volume. Live Concrete curb Curb length, profile, yards, and waste allowance. Live Concrete cost Bagged vs ready-mix material cost and installed cost ranges. Live Concrete block (CMU) Block count, mortar bags, wall openings, and material cost. Live Rebar Slab rebar grid: bars, sticks, steel weight, and cost by size. Live
MVP path
Slab is live first. Post holes and footings come next because their formulas and buying decisions are meaningfully different.
Shopping list
Ready to price and order
Use the calculated quantities as a starting cart, then compare store availability, delivery fees, pallet limits, and local ready-mix minimums before buying.
Large pours
Ready-mix quote check
For high bag counts, compare the bagged route against local ready-mix minimums, delivery, access, and unload time.
Optional base
Gravel base
Base depth is project-specific. Estimate it separately before adding bags or bulk gravel to the order.
Optional forms
Forms and stakes
Plan lumber, stakes, screws, release, and bracing around the perimeter and any step-downs or curves.
Store buttons open retailer search results for now. Confirm exact product yield, pickup, delivery, and pallet rules before ordering.
Formula shown
How concrete estimates work
Slabs, footings, and walls
length ft x width ft x thickness ft
Round post holes and columns
pi x radius ft² x depth or height ft
Bags and yards
cubic yards = ft³ / 27; bags = ceil(ft³ with waste / bag yield)
Sources
- Quikrete product yields — bagged concrete mix yield references
- Sakrete bagged concrete references — common bag sizes and concrete mix guidance
- ConcreteNetwork concrete price guide — ready-mix and installed concrete cost context
Sources checked
Checked against
Bag yields checked against Quikrete and Sakrete product specs; price ranges against published concrete cost guides.
How we check our numbersLast updated: June 20, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
FAQ
Concrete calculator questions
Quick answers for choosing the right shape, comparing bags and ready-mix, and using waste allowance.
What concrete calculator should I use first? + -
Use the slab calculator for patios, shed pads, walkways, and small rectangular pours. Use post-hole or footing calculators when the shape is different enough to change the formula.
How many bags of concrete are in a cubic yard? + -
A cubic yard is 27 cubic feet. At the published yields of about 0.6 cu ft per 80 lb bag, 0.45 cu ft per 60 lb bag, and 0.3 cu ft per 40 lb bag, one yard takes 45 bags of 80 lb, 60 bags of 60 lb, or 90 bags of 40 lb, before waste.
Do these numbers match the Quikrete and Sakrete calculators? + -
Bag counts use the same published bag yields that Quikrete and Sakrete print on their bags, so the base quantity matches. This calculator then adds a waste allowance (10% by default, editable), which is why its bag count can be a few bags higher.
Should I compare bags and ready-mix? + -
Yes. Bagged concrete is convenient for small work, while ready-mix is usually easier for larger pours. The hub keeps both views visible so you can compare before buying.
Do concrete calculators include waste? + -
MeasureTwice defaults to a 10% waste allowance, but each concrete calculator lets you type a custom percentage for your jobsite or quote comparison. Uneven subgrade, spillage, and form variation can all change final quantities.
Are these estimates a contractor quote? + -
No. The calculators are estimating tools for planning quantities and rough material cost. Verify product yield, price, delivery minimums, and site conditions with your supplier or contractor.