How to calculate concrete
Every concrete estimate is the same three steps: measure the pour in feet, multiply to get cubic feet, then divide by 27 to get cubic yards — because there are 27 cubic feet in a cubic yard. Add about 10% for waste (spillage, uneven subgrade, forms that spread a little), and round up when you order. Running short mid-pour creates a cold joint, which is a weak spot you can't fix later.
cubic feet = length × width × (thickness in inches ÷ 12)
cubic yards = cubic feet ÷ 27
order amount = cubic yards × 1.10 (waste)
How many bags of concrete do I need?
Bagged concrete (like QUIKRETE) lists its yield right on the bag. The published yields are:
80-lb bag → 0.60 ft³ · 60-lb bag → 0.45 ft³ · 40-lb bag → 0.30 ft³
Divide your total cubic feet by the yield and round up — you can't buy half a bag. One full cubic yard takes 45 eighty-pound bags (27 ÷ 0.60). A 10×10 slab at 4 inches thick is 33.3 ft³, or 1.23 cubic yards — about 56 eighty-pound bags before waste.
Bags vs. ready-mix: the 0.5-yard rule
Small jobs go faster and cheaper with bags; big jobs need a ready-mix truck. The breakeven most contractors use is half a cubic yard: below ~0.5 yd³, buy bags; above it, call a truck. Bags cost more per yard (you're paying for the bagging and the retail shelf), but a truck has minimums and short-load fees — typically $50–200 extra if you order under about 3 yards. The calculator above applies this rule automatically and shows you the math both ways.
How much does concrete cost in 2026?
Ready-mix prices vary by region. As rough 2026 estimates: the Northeast and West Coast run around $160–200 per cubic yard, while the Southeast and Midwest are closer to $120–150. Bagged 80-lb concrete mix typically runs $4.50–6 per bag at home centers. These are estimates — delivery distance, PSI strength, admixtures and short-load fees all move the number, so always get a local quote before you budget. Use the regional presets in the calculator as a starting point and edit them to match your quote.
Buying bags? An 80-lb bag covers 0.60 ft³ — for a small patio you'll be hauling dozens of them. A wheelbarrow, a mixing tub or a rented mixer, and a spare pair of hands are worth more than any gadget. (Retail links coming soon.)
Tips before you pour
- Thickness matters: 4 inches is standard for patios and walkways; driveways want 5–6 inches; anything carrying heavy loads goes thicker with rebar.
- Order a touch extra: 10% waste is the default here for a reason — forms flex and subgrade is never perfectly level.
- One cubic yard weighs about 4,050 lb — plan your trailer and your back accordingly.
- Concrete ≠ cement. Cement is the gray powder; concrete is cement plus water, sand and gravel. You order concrete, not cement.
- Combine pours: a slab plus its footings is one order. Use the project total above so the plant gets a single number.
Frequently asked questions
How many 80-lb bags are in a cubic yard?45. A cubic yard is 27 cubic feet, and an 80-lb bag of concrete mix yields 0.60 ft³ (per QUIKRETE's published specs). 27 ÷ 0.60 = 45 bags exactly. Add 10% waste and you're at about 50 bags for a real-world yard.
How much concrete do I need for a 10×10 slab?At 4 inches thick: 10 × 10 × (4 ÷ 12) = 33.3 ft³, which is 1.23 cubic yards — about 56 eighty-pound bags. With 10% waste, plan on 1.36 yards or 62 bags. At 6 inches thick it becomes 50 ft³ (1.85 yd³, ~84 bags).
How thick should a concrete slab be?4 inches for patios, walkways and shed floors; 5–6 inches for residential driveways; 6+ inches with rebar reinforcement for RV pads, workshops or anything carrying heavy point loads. Thicker is cheaper than replacing a cracked slab.
When is ready-mix cheaper than bags?Above about half a cubic yard. Below 0.5 yd³, bags win on total cost and convenience. Above it, a ready-mix truck is cheaper per yard and far less labor. Watch out for short-load fees (often $50–200) on truck orders under ~3 yards.
How much does a yard of concrete cost?Roughly $130–200 per cubic yard in 2026 depending on region — higher on the coasts, lower in the Southeast and Midwest. Strength (PSI), admixtures, delivery distance and short-load fees all add to it. Treat any online figure as an estimate and get a local quote.
What's the difference between concrete and cement?Cement is an ingredient — the fine gray powder that binds everything. Concrete is the finished material: cement plus water, sand and gravel (aggregates). When you order for a slab, you order concrete, measured in cubic yards.
How much does a cubic yard of concrete weigh?About 4,050 pounds. Standard concrete weighs roughly 150 lb per cubic foot, and a yard holds 27 cubic feet (27 × 150 = 4,050). That's why delivery and trailer capacity matter — a "small" order is still two tons.
More concrete calculators
Disclaimer: This calculator provides estimates for planning purposes only — not professional engineering advice. Always verify quantities with your supplier and follow local building codes for footings, structural walls and load-bearing work. Prices shown are 2026 estimates; get a local quote.