How thick should a concrete slab be?

A standard residential slab should be at least 4 inches thick. Driveways need 6 inches for cars and 8 inches for trucks or RVs. Sidewalks are typically 4 inches. Always check local building codes for your specific project.

How many yards of concrete do I need for a 10x10 slab?

A 10×10 foot slab at 4 inches thick requires approximately 1.23 cubic yards of concrete (before adding a waste factor). With 10% waste, order about 1.35 yards. At 6 inches thick, you need about 1.85 cubic yards.

How many bags of concrete for a 10x10 slab?

A 10×10 ft slab at 4 inches thick needs approximately 1.23 cubic yards (33.3 cubic feet). That equals about 84 bags of 60 lb concrete or 63 bags of 80 lb concrete (at standard 150 lb/ft³ density). Add 10% for waste.

Do I need rebar in my concrete slab?

For most residential slabs (patios, sidewalks, garage floors), #3 or #4 rebar on 12–18 inch centers is recommended. Wire mesh is an alternative for light-duty slabs. Structural slabs like foundations always require engineered rebar plans.

How long does a concrete slab take to cure?

Concrete reaches about 70% of its full strength in 7 days and 99% in 28 days. You can typically walk on it after 24–48 hours and drive on it after 7 days. Keep it moist and above 50°F during the first week to ensure proper curing.

How much does a yard of concrete weigh?

One cubic yard of concrete weighs approximately 4,050 pounds (1,837 kg) at standard density of 150 lb/ft³. Since one cubic yard equals 27 cubic feet: 150 × 27 = 4,050 lbs. Lightweight mixes weigh less; high-density or rebar-reinforced mixes weigh more.

What is the difference between concrete and cement?

Cement is an ingredient in concrete — the two are not the same thing. Cement is a fine powder made from limestone and clay that acts as a binding agent. When you mix cement with water, sand, and gravel, you get concrete. A common way to think of it: cement is the glue, concrete is the finished material.

What PSI concrete should I use for a residential slab?

For sidewalks and patios, 3,000 PSI is the standard minimum. For garage floors and driveways, use 3,500–4,000 PSI — vehicle loads and tire impact require higher strength. For any exterior slab in a climate with freezing winters, specify air-entrained concrete with 5–7% air content; this is required by IRC R506.2.2 for slabs exposed to deicing chemicals. Higher PSI also means better abrasion resistance and a harder surface finish.

Do I need rebar in a concrete slab?

For most residential slabs (driveways, patios, garage floors), rebar or wire mesh is strongly recommended though not always code-required. ACI 318 recommends a 0.0018 minimum steel ratio for temperature/shrinkage control in slabs. Use #3 or #4 rebar on 12–18 inch grid for slabs 4–6 inches thick. Wire mesh (6×6-W1.4×W1.4) is a lower-cost alternative for patios but provides less structural benefit. For any slab that will carry vehicle loads, rebar on 12-inch centers is the professional standard.

Concrete Slab Calculator — Cubic Yards, Bags & Cost

Estimates volume and bags for a slab, pad, or floor — including overage and bag count by size.

How to Use This Concrete Slab Calculator

This concrete slab calculator takes three inputs — length, width, and thickness — and instantly returns the volume in cubic yards and cubic feet, the number of bags needed, and an optional cost estimate. It also works as a concrete floor calculator for any indoor poured floor — just enter the room dimensions and desired thickness. Use this material calculator for concrete slab projects to get the exact yardage and bag count before you buy. Enter your slab dimensions above, select your bag size, and adjust the waste factor if needed (10% is standard). For multi-shape projects, see our concrete calculator which handles slabs, columns, footings, and stairs all in one tool.

How to Calculate Concrete for a Slab

Calculating concrete for a slab involves three measurements: length, width, and thickness (depth). The formula is:

Volume (yd³) = Length (ft) × Width (ft) × Depth (ft) ÷ 27

Since thickness is usually measured in inches, convert to feet first by dividing by 12. A 4-inch slab is 0.333 feet; a 6-inch slab is 0.5 feet.

Step-by-Step Example

Measure the length and width of your slab area in feet
Determine the slab thickness (usually 4 or 6 inches)
Enter the dimensions in the calculator above
The calculator automatically adds a 10% waste factor
Read off your cubic yards and bag count

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How Many Bags of Concrete for a Slab?

The number of bags depends on the bag size. Here are some common slab sizes and the bags required:

10×10 at 4 in thick — 1.23 yd³ — about 84 bags (60 lb) or 63 bags (80 lb)
12×12 at 4 in thick — 1.78 yd³ — about 120 bags (60 lb) or 90 bags (80 lb)
20×20 at 4 in thick — 4.94 yd³ — order ready-mix concrete
20×20 at 6 in thick — 7.41 yd³ — order ready-mix concrete

For projects over 1–2 cubic yards, ready-mix concrete delivered by truck is much more cost-effective than bags. For large square footage slabs — driveways, garage floors, or commercial pads — ready-mix is almost always the right choice.

Concrete Slab Cost Estimate

Concrete material costs vary by region, but here are typical price ranges:

Ready-mix concrete: $110–$165 per cubic yard (plus delivery fee)
60 lb bags (Quikrete/Sakrete): ~$5.50–$6.50 per bag
80 lb bags: ~$6.50–$8.00 per bag

Use the cost estimator in the calculator above — enter your local price per cubic yard for an accurate estimate. For a more detailed breakdown of all cost components, try the concrete cost calculator.

What Is Concrete?

Concrete is a composite building material made from four ingredients: Portland cement, water, fine aggregate (sand), and coarse aggregate (gravel or crushed stone). The cement and water form a paste that hardens through a chemical reaction called hydration, binding the aggregates into a mass similar to rock. After 28 days, concrete reaches roughly 99% of its final compressive strength — though it continues to harden for years.

Concrete vs. Cement

Cement and concrete are not the same thing — cement is one ingredient in concrete. Cement is a fine powder made from limestone and clay; on its own it is brittle and prone to cracking. Concrete is the finished material: cement paste combined with sand and gravel. Think of cement as the glue and concrete as the final product.

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Concrete Slab Standards and Code Requirements

Residential concrete slab construction is governed primarily by the International Residential Code (IRC) and ACI 318 (Building Code Requirements for Structural Concrete). Key standards to know:

Minimum thickness — IRC R506.1 requires a 3.5-inch minimum thickness for residential floors on grade; 4 inches is standard practice for patios, sidewalks, and garage floors; driveways should be 6 inches for passenger vehicles
Concrete strength — IRC R506.2.1 requires at least 3,500 PSI for residential slabs exposed to freezing and thawing; 4,000 PSI is recommended for driveways and any slab exposed to deicing salts
Reinforcement — ACI 318 Section 24.4 requires a minimum 0.0018 steel ratio for temperature and shrinkage steel in slabs; for a 4-inch slab, #3 rebar at 18-inch OC satisfies this minimum
Subgrade — IRC R506.2.2 requires a 4-inch gravel base over compacted fill; a 6-mil polyethylene vapor barrier is recommended to prevent moisture migration from the soil into the slab
Control joints — ACI 360 recommends joint spacing of 24–36 times the slab thickness; for a 4-inch slab, joints every 8–12 feet are standard

Tips for Pouring a Concrete Slab

Prepare the subgrade — compact the base and add 4 inches of gravel for drainage
Set forms — use 2×4 or 2×6 lumber and check for level and square
Add rebar or mesh — for any slab that will bear vehicle loads; use our rebar calculator to estimate steel requirements
Order 10% extra — always add waste to your calculated volume
Mix correctly — if mixing on-site, use our concrete mix calculator to get the right cement, sand, and aggregate ratios
Know your weight — before pouring on an elevated surface or deck, use the concrete weight calculator to verify structural load capacity
Cure properly — keep the slab moist for 7 days after pouring

Sources & References

ACI 318-19: Building Code Requirements for Structural Concrete — American Concrete Institute
ASTM C94/C94M: Standard Specification for Ready-Mixed Concrete — ASTM International
PCA: Design and Control of Concrete Mixtures (16th Edition) — Portland Cement Association

Concrete Slab Calculator