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Concrete calculator
Enter the size of your slab, footing, pier or steps and get the cubic yards to order from a ready-mix plant, or the number of 40, 60 or 80 lb bags to buy. Pouring a driveway? Pick what drives on it and get the thickness, base stone and joint spacing too.
Strip footing: enter its full length. Square pad footings: enter the side length in feet, the width and depth in inches, and how many.
Enter sizes greater than zero.
Compare bags vs ready-mix cost
In central PA? Our crews form and pour slabs, footings, piers and steps. See our concrete work.
How it works
Slab: length × width × thickness. Footing: length × width × depth. Pier: π × radius² × depth. Steps: width × rise × tread × (1 + 2 + … + number of steps), plus any top landing.
Everything is worked in feet, so cubic feet ÷ 27 = cubic yards, the unit ready-mix plants sell by. Your waste percentage is added on top.
Cubic feet ÷ the bag’s yield, rounded up: 0.60 cu ft per 80 lb bag, 0.45 per 60 lb and 0.30 per 40 lb, from Quikrete’s Concrete Mix data sheet.
10 × 10 ft slab at 4 in: 10 × 10 × (4 ÷ 12) = 33.3 cu ft
33.3 ÷ 27 = 1.23 cu yd · 33.3 ÷ 0.60 = 55.6 → 56 bags of 80 lb
With 10% extra: 36.7 cu ft = 1.36 cu yd → 62 bags of 80 lb
Quikrete notes that its yields are approximate and don’t allow for an uneven base or waste, which is why the calculator starts at 10% extra. Raise it for hand-dug holes and rough subgrade.
When ready-mix beats bags
Bag cost per yard = 45 × your 80 lb bag price (27 ÷ 0.60 = 45 bags). Break-even yards = the plant’s delivery and short-load fees ÷ (bag cost per yard − ready-mix price per yard). Below it, bags are cheaper; above it, the truck is. Open “Compare bags vs ready-mix cost” above to run your numbers.
Every cubic yard of bagged concrete is 45 bags of 80 lb mix, 3,600 lb to lift and mix, and a slab has to be placed and finished before the first batch stiffens. Ask the plant about its minimum load and whether the chute can reach your forms.
Driveways and parking pads
Pick a driveway use under Slab and the thickness fills in: 4 in. for cars, SUVs and light pickups and 5 in. where delivery trucks or other heavy loads drive, the IRMCA minimums, and 6 in. for a parked RV, camper or work truck, the top of Concrete Network’s 5 to 6 in. You can still type your own. The code floor is 3 1/2 in. (ACI 332-20).
At least 4 in. of compacted crushed stone (IRMCA). Joint spacing in feet runs 2 to 3 times the slab thickness in inches, never over 15 ft, cut at least a quarter of the slab deep within 4 to 12 hours (NRMCA CIP 6).
Where it freezes or sees road salt, at least 4,000 psi with about 6% entrained air (PACA, IRMCA). Where trucks run near the edges, make them 1 to 2 in. thicker for the outer 4 to 8 in. (Concrete Network).
More on bags and yields: How many bags of concrete do I need? Picking a thickness: how thick a concrete patio should be and how thick a concrete driveway should be.
Questions
How many bags of concrete are in a yard?
A cubic yard is 27 cubic feet. At Quikrete’s published yields that is 45 bags of 80 lb mix (0.60 cu ft each), 60 bags of 60 lb mix (0.45 cu ft) or 90 bags of 40 lb mix (0.30 cu ft), before any extra for waste.
How much concrete do I need for a 10×10 slab?
At 4 inches thick, 33.3 cubic feet, or 1.23 cubic yards: 56 bags of 80 lb mix or 75 bags of 60 lb mix before waste. With 10% extra, plan on 1.36 cubic yards or 62 bags of 80s.
How many bags of concrete do I need for a sonotube?
An 8 inch tube filled 4 feet deep holds about 1.4 cubic feet, or 3 bags of 80 lb mix. A 12 inch tube 4 feet deep holds about 3.1 cubic feet, or 6 bags of 80s. How deep the footing goes comes from your local code and frost depth, not from the calculator.
How much extra concrete should I order?
Quikrete notes that its bag yields are approximate and don’t allow for an uneven base or waste. The calculator starts at 10% extra, the allowance our crews plan on slabs. Go higher for hand-dug holes and rough subgrade.
How much area does a yard of concrete cover?
Divide 324 by the thickness in inches: a cubic yard covers 81 square feet at 4 inches, about 65 at 5 inches and 54 at 6 inches.
When should I order ready-mix instead of bags?
When the truck costs less for your yardage, or when you can’t mix and place the pour before the first batch stiffens. Every cubic yard is 45 bags of 80 lb mix, 3,600 lb to lift and mix. Get the plant’s price per yard and its delivery and short-load fees, then compare them in the calculator.
What thickness should I enter for a driveway?
4 inches for cars, SUVs and light pickups, and at least 5 inches where delivery trucks or other heavy loads will drive, per the Illinois Ready Mixed Concrete Association. For a parked RV, camper or work truck, Concrete Network puts it at 5 to 6 inches. Pick the use in the calculator and it fills in the thickness and shows the base stone and joint spacing.
Sources: Quikrete Concrete Mix No. 1101 data sheet (yields: 40 lb 0.30 cu ft, 60 lb 0.45 cu ft, 80 lb 0.60 cu ft); Sakrete High-Strength Concrete Mix 80 lb (yield 0.6 cu ft); Quikrete calculator (yields approximate, no allowance for uneven substrate or waste); driveway figures: Illinois Ready Mixed Concrete Association, Concrete Guide for Residential Exterior Flatwork (4 in. minimum, 5 in. for heavy loads, 4 in. base, 6% air); Tennessee Concrete Association, ACI 332-20 highlights (3 1/2 in. minimum); Concrete Network, driveway thickness (5 to 6 in. for heavy trucks and RVs, thickened edges); NRMCA CIP 6, Joints in Concrete Slabs on Grade; Pennsylvania Aggregates and Concrete Association, Protecting Concrete From Deicer Damage (4,000 psi). 1 cu yd = 27 cu ft; 1 cu ft = 0.0283 m³.
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