Concrete Calculator: How Much Concrete Do I Need?

Measure length × width × thickness in feet, then divide by 27 to get cubic yards: (L × W × (T/12)) ÷ 27. For example, a 10 ft × 10 ft slab at 4 in thick is 10 × 10 × 0.333 = 33.33 cu ft, which is 1.24 cubic yards. This calculator does that math for 8 shapes automatically, converts to cu ft, cu yd and m³, and adds a waste factor you choose.

One cubic yard (27 cu ft) needs about 45 bags of 80-lb mix, 60 bags of 60-lb mix, 72 bags of 50-lb mix, or 90 bags of 40-lb mix. Those are round figures — in practice you always round up to the next whole bag, so 1.24 cubic yards needs 56 bags of 80-lb mix. The bag comparison table on this page computes exact counts for every bag size.

Published yields (Quikrete concrete mix): an 80-lb bag yields 0.60 cu ft, a 60-lb bag yields 0.45 cu ft, a 50-lb bag yields 0.375 cu ft, and a 40-lb bag yields 0.30 cu ft. This tool uses these published figures. The 30 kg (~66 lb) bag common in Australia and the UK is treated as the linear equivalent of the 80-lb yield (~0.50 cu ft) — stated as an estimate, since published yields vary slightly by brand and mix design.

Almost always above about 1–2 cubic yards. Bags cost roughly $240–$250 per yard equivalent (e.g. 56 eighty-pound bags at $5.50 = $308 for 1.24 yd³), while ready-mix typically costs $130–$160 per yard plus a $50–$100 delivery fee — so the same 1.24 yd³ costs about $233 by truck. The crossover advisor on this page compares both options for your exact pour and shows the break-even yardage.

Add 5–10% for most DIY pours. Subgrade settles, forms flex, and spillage happens — ordering exactly the calculated volume usually leaves you short. This calculator applies your waste percentage before counting bags, and the default is 5%. Use 10% for irregular excavations like hand-dug footings or post holes.

Treat it as a cylinder: volume = π × r² × h, all in feet. For a 12-in-diameter tube 4 ft deep: π × 0.5² × 4 = 3.14 cu ft (0.12 cu yd), which needs 6 bags of 80-lb mix. Select the Sonotube/Pier mode, enter the tube diameter and depth, and the calculator handles it — including a quantity of holes at once.

Each step is a rectangular block whose height grows step by step: volume = rise × run × width × (1 + 2 + … + n), or equivalently rise × run × width × n(n+1)/2. For 5 steps with a 7-in rise, 11-in run, and 4-ft width that is about 32.1 cu ft (1.19 cu yd) — 54 bags of 80-lb mix. The Steps mode computes this and counts the bags.

Plan on about 0.2 cubic feet of grout per standard 8×8×16-inch block — an assumption this calculator states up front, since actual core volume varies by block manufacturer. 100 filled blocks need about 20 cu ft (0.74 cu yd), or 34 bags of 80-lb mix. For partially grouted walls (every other core), enter half your block count.

Multiply the cross-section area by the length: volume = length × (curb width × curb height + gutter width × gutter thickness) ÷ 144. A 50-ft run with a 6×6-in curb and an 18×4-in gutter pan needs 37.5 cu ft (1.39 cu yd), or 63 bags of 80-lb mix. The Curb & Gutter mode takes your section dimensions directly.

27. A cubic yard is a 3 ft × 3 ft × 3 ft cube. One cubic yard of concrete weighs about 4,000 lb (roughly 2 tons) and covers about 81 sq ft at 4 in thick. A cubic yard is also 0.765 cubic meters. This page shows every result in cu ft, cu yd, and m³ side by side.

Ready-mix typically runs $130–$160 per cubic yard plus a $50–$100 delivery fee in the US, but prices vary widely by region, fuel surcharges, short-load fees, and minimums (many plants charge extra for loads under 3–4 yards). Bagged mix is priced per bag at your store. Because prices move, this calculator lets you enter your local per-bag price, per-yard price, and delivery fee instead of hard-coding numbers.

First get cubic feet: area in sq ft × (thickness in inches ÷ 12). Then divide by 27. Worked example for a 10×10 driveway slab at 4 in: 100 sq ft × 0.333 ft = 33.33 cu ft ÷ 27 = 1.24 cu yd. Round up, then add your waste factor — never order exactly the calculated number.

Yes. Switch to metric and enter meters and centimeters; results show cubic meters alongside cu ft and cu yd. For Australia and the UK, the bag comparison includes 30-kg bags (the common local size), and the answers above cover "concrete bag calculator kg" style queries — enter 50 kg per bag equivalents by comparing yields.

A monolithic slab is one pour: the slab plus a thickened edge footing around the perimeter. Volume = slab volume + (perimeter length × edge width × edge depth). A 20×20-ft slab at 4 in with a 12×12-in edge needs about 213 cu ft (7.9 cu yd). Select Slab mode, turn on the thickened edge option, and enter the edge width and depth.

It is as exact as your measurements — the math is deterministic — but real pours vary: subgrade compresses, forms bow outward, and excavations are rarely perfect rectangles. That is why the 5–10% waste factor exists. For structural footings, columns, and anything load-bearing, have your design checked against local code by a qualified professional; this tool estimates material, not structural adequacy.

Yes. This concrete calculator runs 100% in your browser — every calculation happens on your device and nothing is sent to any server. There are no accounts, no tracking of your projects, and it keeps working offline after the first load.