What is Concrete Calculator?

The Concrete Calculator estimates the volume of concrete needed for slabs, footings, columns, walls, and stair pours. Enter your dimensions and get precise results in cubic yards, cubic meters, and number of bags needed.

The calculator handles four pour shapes — flat slab or footing, cylindrical column, wall or footer, and stair steps (riser plus run plus optional top platform) — and lets you stack several sections into one project so a slab, footer, and column pour add up to a single grand total. Each shape ships with a labeled diagram so you can match Length, Width, Depth, Diameter, Rise, and Run to the right input. Toggle between US units (feet and inches) and metric (meters). Results show in cubic yards, cubic meters, and cubic feet, plus the number of 40, 50, 60, and 80 pound bagged mix needed at standard yield (about 0.011, 0.014, 0.017, and 0.022 yd³ per bag).

How to use

1. Step 1 — Add one section per pour, then pick its shape: slab / square footing, cylindrical column, wall / footer, or stairs. Combine several sections for a driveway-plus-footer or slab-plus-column project in one estimate.
2. Step 2 — Enter length, width, and depth (or diameter and height for columns) in your preferred unit.
3. Step 3 — Read the volume in cubic yards, cubic meters, and cubic feet, plus the weight, estimated cost, and bag counts for 40, 50, 60, and 80 pound mixes. Multi-section projects also show a Project Totals card with the grand total.

When to use

• Quoting a patio, driveway, or garden path before ordering ready-mix or bagged concrete.
• Estimating how many fence post or deck pier columns one truck of premix will fill.
• Checking a contractor's bag count against the actual pour volume to avoid overordering.

Result

A homeowner building a 10ft × 12ft patio at 4 inches thick enters the dimensions and gets 1.48 cubic yards — approximately 30 bags of 80-lb concrete mix.

FAQ

Should I add a waste allowance to the result?

Yes. Most contractors add 5 to 10% to cover spillage, uneven subgrade, and form leaks. For an irregular hand-dug footing, bump it up to 15%. The calculator gives the pure geometric volume, not a job-site estimate.

Why do bag counts differ between 40, 50, 60, and 80 lb bags?

Yield scales with weight: a 40 lb bag makes about 0.3 ft³, a 50 lb bag about 0.375 ft³, a 60 lb bag about 0.45 ft³, and an 80 lb bag about 0.6 ft³. For pours under one cubic yard, 80 lb bags are usually cheaper per yd³, but heavier to carry. The 50 lb size is common at Quikrete and Sakrete and lands in the sweet spot for one-person handling.

How thick should a residential slab be?

Patios and shed pads are usually 4 inches. Driveways for passenger cars are 4 to 5 inches; for trucks or RVs, 6 inches. Garage slabs follow local code but 4 inches over a compacted base is the common minimum.

When does it make sense to order ready-mix instead of bags?

Above roughly one cubic yard, bagged mix becomes labor-intensive (45 bags of 80 lb for one yard). A short-load delivery from a ready-mix plant is usually cheaper and finished in one pour, which is better for slab integrity.

Does the column formula account for rebar or pipe inserts?

No. The result is the raw cylinder volume πr²h. Subtract the displacement of any large embedment (a 4 inch sleeve in a 12 inch column removes about 11% of the volume). For thin rebar the difference is negligible.

Related Tools