Concrete Calculator — How Much Concrete Do I Need?
Select your shape, enter dimensions, and instantly calculate cubic yards, bag counts, reinforcement, and cost.
🧱 Concrete Calculator
ℹ️ Select a standard sonotube size or enter a custom diameter. Formula: π × (diameter/2)² × depth × number of tubes.
ℹ️ Typical residential stairs: 7" rise, 11" run, 36"–48" wide. Platform adds a landing slab at the top step.
ℹ️ Cross-section area × length. Curb body = curb width × (curb depth + curb height). Flag = flag width × flag thickness. Gutter = gutter width × flag thickness.
How to Use This Concrete Calculator
Getting the right amount of concrete is one of the most important steps in any slab, footing, or flatwork project. Order too little and you'll scramble to fill gaps before the initial pour sets. Order too much and you're paying for concrete that will need to be hauled away. This calculator makes it straightforward.
- Choose your unit system. Toggle between Imperial (feet and inches) and Metric (meters and centimeters) using the buttons at the top of the calculator.
- Enter the length and width. Measure the longest dimension of your pour area in feet (or meters). For an irregular shape, break it into rectangles and use the "Number of Areas" field to multiply identical sections.
- Enter the depth or thickness. Measure or specify your slab thickness in inches (or centimeters). Common values are 3.5 inches for sidewalks, 4 inches for driveways and patios, and 8–12 inches for footings.
- Set the number of areas. If you have multiple identical pour sections — like 5 identical footings — enter 5 here. The calculator multiplies the volume accordingly.
- Read your results. You'll instantly see cubic yards, cubic feet, and cubic meters. Bag counts include a built-in 10% waste factor so you don't run short. Enter a price per cubic yard to see an estimated total cost.
Pro tip: Always round up when ordering ready-mix concrete. Most plants sell in quarter-yard increments, and it's far better to have a small amount left over than to come up short mid-pour.
Most concrete slabs require a compacted gravel base beneath them. You'll also need a gravel sub-base — see our Gravel Calculator to estimate how much material you'll need before the concrete goes in.
Concrete Calculation Formulas
The math behind concrete volume is simple — you're just calculating the volume of a rectangular box and converting it to the unit your supplier uses.
Imperial Formula (feet and inches)
Step 2: Calculate cubic feet → Volume (ft³) = Length × Width × Depth (ft)
Step 3: Convert to cubic yards → Volume (yd³) = Volume (ft³) ÷ 27
Example: A 10 ft × 10 ft slab at 4 inches thick:
Cubic feet = 10 × 10 × 0.333 = 33.33 ft³
Cubic yards = 33.33 ÷ 27 = 1.23 yd³
Metric Formula (meters and centimeters)
Step 2: Volume (m³) = Length (m) × Width (m) × Depth (m)
Step 3: Convert to cubic yards → Volume (yd³) = Volume (m³) ÷ 0.7646
Why 27?
There are 27 cubic feet in one cubic yard (3 ft × 3 ft × 3 ft = 27 ft³). Ready-mix concrete is sold by the cubic yard in the US, so this conversion is essential. In Canada and most other countries, concrete is ordered by the cubic meter.
Bag Calculation Formula
Bags per cubic yard (including 10% waste):
60 lb bags: (yd³ × 1.10) × 60 bags/yd³
40 lb bags: (yd³ × 1.10) × 80 bags/yd³
These ratios come from the stated yield on standard bags: an 80 lb bag yields 0.60 ft³, a 60 lb bag yields 0.45 ft³, and a 40 lb bag yields approximately 0.33 ft³.
Concrete Buying Guide
Once you have your cubic yard number, the next decision is how to buy the concrete. You have two main options: ready-mix (delivered by truck) or bagged concrete that you mix yourself.
Ready-Mix Concrete
Ready-mix is concrete pre-mixed at a batch plant and delivered in a rotating drum truck. It's the right choice for any project over about 1 cubic yard.
- Cost: $150–$200 per cubic yard delivered, depending on your location, mix design, and distance from the plant. Expect extra charges for short loads (less than a full truck, usually 7–10 yards).
- Minimum orders: Most plants have a minimum of 1 yard. Short-load fees ($50–$100 per missing yard) apply if you order less than their minimum.
- Mix design: Specify 3,000–3,500 PSI for residential slabs. Tell the plant your application (driveway, footing, sidewalk) and they'll recommend the right mix.
- How to order: Call 2–3 days ahead. Have your cubic yard total ready, plus the address and pour date. Confirm your pour window — trucks are typically in and out in 7–10 minutes per yard.
Bagged Concrete
Bagged concrete (Quikrete, Sakrete, or similar) is the right choice for small projects under 1 cubic yard — footings for fence posts, small repairs, stepping stones, or a single small slab.
- Cost: $8–$12 per 80 lb bag at home improvement stores. At that price, 45 bags for 1 cubic yard costs $360–$540 — significantly more than ready-mix.
- Labor: Each 80 lb bag requires mixing by hand or in a small electric mixer. Budget 5–10 minutes per bag including mixing and pouring.
- When to use bags: Projects under 1 yard, repairs, fence posts, deck footings, or any project where ready-mix truck access is impossible. For fence post holes, check the Fence Calculator to plan your footings. Building deck footings? Try our Decking Calculator for lumber estimates too.
- Storage: Unused bags must stay dry. Even a small amount of moisture will start the curing process and render bags unusable.
Concrete Prices by Region (2026)
Ready-mix prices vary significantly by location. These are approximate ranges:
- Northeast (NY, MA, CT): $180–$220/yd³
- Southeast (FL, GA, NC): $140–$170/yd³
- Midwest (OH, IL, MI): $130–$160/yd³
- South-Central (TX, OK): $125–$155/yd³
- West Coast (CA, WA, OR): $160–$200/yd³
- Mountain West (CO, UT, AZ): $140–$175/yd³
These prices typically include delivery within 10 miles of the plant. Long-distance surcharges and fuel surcharges are common, especially in rural areas.
Common Project Sizes
Here are typical concrete volumes for common residential and commercial projects. Use these as benchmarks to sanity-check your calculator result.
| Project | Typical Dimensions | Depth | Cubic Yards | 80 lb Bags | Use Ready-Mix? |
|---|---|---|---|---|---|
| Sidewalk (residential) | 3 ft × 30 ft | 3.5 in | 1.09 | 54 | Borderline — yes |
| Patio (medium) | 12 ft × 16 ft | 4 in | 2.37 | 117 | Yes |
| Patio (large) | 20 ft × 24 ft | 4 in | 5.93 | 293 | Yes |
| Driveway (single car) | 10 ft × 20 ft | 4 in | 2.47 | 122 | Yes |
| Driveway (double car) | 20 ft × 24 ft | 5 in | 9.26 | 458 | Yes |
| Garage floor | 20 ft × 24 ft | 4 in | 5.93 | 293 | Yes |
| Shed slab | 8 ft × 10 ft | 4 in | 0.99 | 49 | Borderline |
| Fence post footing | 10 in × 10 in | 24 in deep | 0.05 | 3 | No — use bags |
| Concrete steps (3-step) | 4 ft × 6 ft | 8 in avg | 0.59 | 29 | No — use bags |
| House foundation (strip) | 100 ft run | 8 in × 18 in | 11.11 | 550 | Yes — always |
ℹ️ Cubic yard totals are base volumes without waste factor. Bag counts include 10% waste.
Sonotube / Form Tube Fill Chart
How many 80 lb bags of concrete do you need for a sonotube (form tube) post footing? Use this quick reference. Values assume an 80 lb bag yields 0.60 cubic feet and include no waste factor — buy 1 extra bag per footing as buffer.
Formula: Volume (ft³) = π × (diameter ÷ 24)² × depth (ft) | Bags = Volume ÷ 0.60, rounded up
| Tube Diameter | Depth 24" (2 ft) | Depth 36" (3 ft) | Depth 48" (4 ft) |
|---|---|---|---|
| 8" | 2 bags (80 lb) | 2 bags (80 lb) | 3 bags (80 lb) |
| 10" | 2 bags (80 lb) | 3 bags (80 lb) | 4 bags (80 lb) |
| 12" | 3 bags (80 lb) | 4 bags (80 lb) | 6 bags (80 lb) |
| 14" | 4 bags (80 lb) | 6 bags (80 lb) | 8 bags (80 lb) |
| 16" | 5 bags (80 lb) | 7 bags (80 lb) | 10 bags (80 lb) |
| 18" | 6 bags (80 lb) | 9 bags (80 lb) | 12 bags (80 lb) |
| 24" | 11 bags (80 lb) | 16 bags (80 lb) | 21 bags (80 lb) |
ℹ️ Bag counts are ceiling values based on exact volume. Buy one extra bag per footing for spills and overfill. Most deck footings use 10"–12" sonotubes at 36"–48" depth in frost-prone climates.
What PSI Concrete Do I Need?
PSI stands for pounds per square inch — the compressive strength of cured concrete after 28 days. It's the single most important spec to communicate to your ready-mix supplier or to look for on a bag. Higher PSI means stronger, denser concrete that resists cracking, freeze-thaw cycles, and heavy loads.
Here's the practical guide:
| PSI Rating | Grade | Best For |
|---|---|---|
| 2,500 PSI | Light-duty | Walkways, patios, light foot-traffic slabs (residential minimum) |
| 3,000 PSI | Standard residential | Driveways, garage floors, general slabs — the most common choice |
| 3,500 PSI | Heavy-duty residential | Driveways that regularly support heavy vehicles (trucks, RVs, trailers) |
| 4,000 PSI | Commercial | Parking lots, loading docks, equipment pads, high-traffic surfaces |
| 4,500+ PSI | Structural | Foundations, load-bearing columns, bridge decks, engineered structures |
For most homeowners, 3,000 PSI is the right default. It's what virtually every ready-mix plant stocks and what all-purpose bagged mixes (Quikrete 5000, Sakrete High-Strength) are rated at. Stepping up to 3,500 or 4,000 PSI typically adds $5–$15 per cubic yard but meaningfully extends the life of your slab in cold climates or heavy-use applications.
One more thing PSI doesn't cover: fiber reinforcement and air entrainment. In freeze-thaw climates (anywhere that sees extended winters), specify air-entrained concrete — small air bubbles that give water room to expand as it freezes. This prevents the surface scaling that ruins otherwise solid concrete.
Frequently Asked Questions
A 10×10 ft slab at 4 inches thick requires 1.23 cubic yards of concrete. The math: 10 × 10 × (4 ÷ 12) ÷ 27 = 1.23 yd³. When ordering ready-mix, add 10% and round up — so order 1.4 cubic yards. If using bags, you'll need about 62 × 80-pound bags (including waste).
You need 45 bags of 80 lb concrete mix per cubic yard (before waste). Each 80 lb bag yields 0.60 cubic feet, and there are 27 cubic feet per cubic yard. With the standard 10% waste allowance, budget for 50 bags per cubic yard to be safe. At $8–$12 per bag, that's $400–$600 per yard — much more expensive than ready-mix for larger jobs.
The standard rule: use bags for anything under 1 cubic yard, ready-mix for anything over 1 yard. Bags give you full control of timing and mixing speed, which is great for small pours and repairs. Ready-mix is faster, more consistent, and significantly cheaper per yard for larger projects — the break-even point is roughly 1–1.5 yards depending on your area. Also consider truck access: ready-mix trucks are large and need a clear path to the pour site.
Standard thickness guidelines:
- Residential driveways: 4 inches minimum; 5–6 inches if heavy vehicles (trucks, RVs) will park on it
- Patios and pool decks: 3.5–4 inches
- Sidewalks and walkways: 3.5–4 inches
- Garage floors: 4 inches minimum; 5 inches for better durability
- Structural footings: 8–12 inches deep depending on local frost depth and load — always check local building codes
Thicker is always stronger, but also more expensive. Don't go below the minimums — thin concrete cracks under load.
One cubic yard is a cube measuring 3 ft × 3 ft × 3 ft — roughly the size of a washing machine or small dishwasher. It weighs approximately 4,000 pounds (2 tons). Spread at different thicknesses, one cubic yard covers:
- 3.5 inches thick → 93 sq ft (about 9.6 × 9.6 ft)
- 4 inches thick → 81 sq ft (about 9 × 9 ft)
- 5 inches thick → 65 sq ft
- 6 inches thick → 54 sq ft
For circular slabs or stepping stones, use the circle volume formula: Volume = π × r² × thickness, where r is the radius in feet and thickness is in feet (divide inches by 12).
Example — 4 ft diameter stepping stone (2 ft radius) at 3 inches thick:
Volume = 3.14159 × 2² × (3/12) = 3.14159 × 4 × 0.25 = 3.14 cubic feet = 0.116 cubic yards
For multiple identical circles, multiply by the count. Our rectangular calculator doesn't handle circles — use the formula above for round projects.