Concrete Calculator — Free Concrete Yard & Bag Estimator
Instantly calculate cubic yards, number of bags, and total cost for any concrete pour.
Related Tools
A concrete calculator takes the guesswork out of every pour. Whether you're laying a patio slab, setting fence posts, building a foundation wall, or pouring column footings, getting the right volume of concrete is critical — too little means a second trip to the store, and too much wastes money. This free tool calculates cubic yards, number of bags (40, 60, or 80 lb), and total project cost with a built-in waste factor, instantly and accurately.
How to Use the Concrete Calculator — Step by Step
Using a concrete calculator is straightforward when you know your project dimensions. Here's the exact process:
- Select your shape — Slab, Column, Footing, Post Hole, or Wall.
- Choose pour method — Bags (bagged concrete) or Ready-Mix (bulk cubic yards delivery).
- Enter dimensions — The form shows only the fields relevant to your shape, so there's no confusion.
- Set waste percentage — The default 10% accounts for spillage, uneven subgrade, and contractor overrun. For complex pours, use 15%.
- Add prices optionally — Enter a price per bag or per cubic yard for an instant cost estimate.
- Click Calculate — Get cubic feet, cubic yards, total with waste, bag count, and cost in one click.
The waste factor is critical. Professional contractors always order extra concrete because even a slightly uneven subgrade or a miscalculation can leave you short — and a second ready-mix truck delivery costs a significant fee.
Concrete Calculator for Slabs — Formula & Example
The concrete calculator for a slab uses a simple rectangular volume formula. Slabs are the most common residential concrete pour — patios, driveways, garage floors, and sidewalks all use this method.
Concrete Calculator Volume Formula for Slabs
The formula for slab volume is:
Volume (cu ft) = Length (ft) × Width (ft) × Thickness (ft)
Cubic Yards = Volume (cu ft) ÷ 27
Note: Convert thickness from inches to feet by dividing by 12. A 4-inch slab = 4/12 = 0.333 ft.
Worked example — 10×10 ft slab at 4 inches thick:
- Volume = 10 × 10 × (4÷12) = 10 × 10 × 0.333 = 33.33 cu ft
- Cubic yards = 33.33 ÷ 27 = 1.23 cu yd
- With 10% waste = 1.23 × 1.10 = 1.36 cu yd
- 80 lb bags needed = ⌈1.36 ÷ 0.022⌉ = 62 bags
Concrete Calculator Square Feet — Quick Reference
Use this table to quickly estimate cubic yards by square footage and thickness — useful for fast job-site estimates before using the full concrete calculator:
| Area (sq ft) | 4 in thick (cu yd) | 6 in thick (cu yd) | 8 in thick (cu yd) |
|---|---|---|---|
| 50 | 0.62 | 0.93 | 1.23 |
| 100 | 1.23 | 1.85 | 2.47 |
| 200 | 2.47 | 3.70 | 4.94 |
| 400 | 4.94 | 7.41 | 9.88 |
| 500 | 6.17 | 9.26 | 12.35 |
| 1000 | 12.35 | 18.52 | 24.69 |
Concrete Yard Calculator — Cubic Yards to Bags
The concrete yard calculator converts your project volume into the number of bags or ready-mix yards needed. One cubic yard equals 27 cubic feet and is the standard unit for ordering ready-mix concrete. Understanding this conversion is key to ordering correctly.
One cubic yard of mixed concrete covers approximately 81 square feet at 4 inches thick, or 54 square feet at 6 inches thick. Use the table above for quick lookups, then use the calculator above for exact project-specific quantities.
Bag Concrete Calculator — How Many Bags Do You Need?
The bag concrete calculator tells you exactly how many bags to buy based on your chosen bag size. Each bag size yields a different volume of mixed concrete:
| Bag Size | Yield per Bag | Bags per cu yd | Approx. Cost/yd |
|---|---|---|---|
| 80 lb | 0.022 cu yd | ≈ 45 bags | $270–$360 |
| 60 lb | 0.017 cu yd | ≈ 59 bags | $295–$413 |
| 40 lb | 0.011 cu yd | ≈ 91 bags | $364–$546 |
The 80 lb bag is the most cost-effective per cubic yard and is what most contractors use for large hand-mixed pours. The 40 lb bag is ideal for small repairs, post holes, or situations where heavy lifting is a concern — perfect for solo DIY projects. Always use Math.ceil() to round up bag counts — you can never buy half a bag.
For project reference: a typical 10×10 ft, 4-inch slab with 10% waste requires 62 bags of 80 lb concrete, 80 bags of 60 lb, or 124 bags of 40 lb concrete. This concrete yard calculator verified those numbers using the raw unrounded volume for precision.
Concrete Calculator Price — Cost Estimation
The concrete calculator price feature helps you budget before you buy. Enter a price per bag or per cubic yard to see total project cost instantly. Here's what to expect for typical pricing in the United States:
- Bagged 80 lb concrete: $5–$8 per bag at hardware stores. For our 10×10 slab example (62 bags), expect $310–$496 in materials alone.
- Ready-mix concrete: $120–$200 per cubic yard delivered, depending on region and mix design. A 1.36 cu yd pour at $150/yd costs $204.
- Minimum delivery charges: Most ready-mix companies have a minimum of 1 cubic yard, and short-load fees apply for orders under the truck's minimum (usually 3–5 yards).
For pours under 1 cubic yard, bagged concrete is almost always more practical even if slightly more expensive per yard — you avoid delivery fees and scheduling delays. For anything over 2 cubic yards, ready-mix delivers better value and far less labor.
How to Calculate Concrete Volume for Any Shape
Every shape in the concrete calculator uses a proven geometric formula:
| Shape | Formula (cu ft) | ÷ 27 for cu yd |
|---|---|---|
| Slab | L × W × (T_in ÷ 12) | Yes |
| Column | π × (D_in ÷ 24)² × H | Yes |
| Footing | L × FootingW × Depth | Yes |
| Post Hole | π × (D_in ÷ 24)² × Depth | Yes |
| Wall | L × H × (T_in ÷ 12) | Yes |
Columns and post holes use the cylinder formula. The radius in feet = Diameter_inches ÷ 24 (convert inches to feet then halve). For a 12-inch diameter column at 4 feet tall: π × (0.5)² × 4 = 3.1416 cu ft ÷ 27 = 0.116 cu yd.
Need to calculate footing dimensions separately? Use our Concrete Footing Calculator for detailed footing design. If your project also involves base material, our Gravel Calculator estimates gravel volume and cost for subbase preparation.
For a deeper understanding of concrete mix design, compressive strength, and curing science, see the Wikipedia article on Concrete. For current bagged concrete pricing and product selection, visit Home Depot's concrete section.
Frequently Asked Questions
For a 10×10 ft slab at 4 inches thick, you need approximately 1.23 cubic yards of concrete. With a recommended 10% waste factor, order about 1.36 cubic yards. That equals roughly 62 bags of 80 lb, 80 bags of 60 lb, or 124 bags of 40 lb concrete. Use the calculator above for other thicknesses.
One cubic yard of concrete requires approximately 45 bags of 80 lb (each yields 0.022 cu yd), 59 bags of 60 lb (each yields 0.017 cu yd), or 91 bags of 40 lb (each yields 0.011 cu yd). These yields are based on standard dry-mix concrete — actual yields may vary slightly by brand.
A 4×4 ft slab at 4 inches thick needs about 0.20 cubic yards. With 10% waste, that's 0.22 cubic yards, requiring 10 bags of 80 lb concrete (Math.ceil(0.22 ÷ 0.022) = 10). This is a perfect small DIY project that can be done with bagged concrete and a bucket or small mixer.
Ready-mix concrete typically costs $120–$200 per cubic yard depending on your location, mix design (PSI rating), and order quantity. Delivery fees, short-load charges, and Saturday surcharges add extra cost. Bagged concrete costs roughly $150–$280 per cubic yard in materials, making ready-mix more economical for larger pours.
Use the cylinder formula: Volume (cu ft) = π × (Diameter_ft ÷ 2)² × Height_ft. Divide by 27 for cubic yards. Example: 12-inch diameter (1 ft), 4 ft tall column = π × (0.5)² × 4 = 3.14 cu ft ÷ 27 = 0.116 cu yd. With 10% waste = 0.13 cu yd = 6 bags of 80 lb. The calculator handles this automatically.
One cubic yard of concrete covers: 81 sq ft at 4 inches thick, 54 sq ft at 6 inches thick, 40.5 sq ft at 8 inches thick, or 324 sq ft at just 1 inch thick. The thicker the slab, the less area one yard covers. Use this as a rough check against your concrete calculator results.
A 12-inch diameter post hole that is 3 feet deep needs about 0.087 cubic yards (≈ 4 bags of 80 lb). A standard 10-inch diameter, 2-foot deep hole needs about 0.040 cubic yards (2 bags). Use the Post Hole option in the concrete calculator above — it uses the cylinder formula automatically with your entered diameter and depth.
Ready-mix is usually cheaper per cubic yard for pours over 1–2 yards. Bagged concrete costs roughly $150–$280 per cubic yard in materials vs $120–$200 per cubic yard delivered as ready-mix. However, for pours under 1 yard, bags offer more flexibility — no minimum order, no delivery scheduling, and no short-load fees. For large projects (driveways, foundations), always choose ready-mix.