How Much Concrete Do I Need?

The most common mistake DIYers make with concrete is underestimating the volume. Concrete is sold by the cubic yard, but most people think in square feet. The missing piece is thickness. A 10×10 patio is 100 square feet, but at 4 inches thick it needs 1.23 cubic yards. At 6 inches, it needs 1.85 cubic yards. That is a 50% difference in material and cost.

Here is the exact formula contractors use:

• Step 1: Measure length and width in feet. Multiply them to get square footage.
• Step 2: Measure thickness in inches. Divide by 12 to convert to feet.
• Step 3: Multiply square footage by thickness (in feet) to get cubic feet.
• Step 4: Divide cubic feet by 27 to get cubic yards.
• Step 5: Add a 5–10% waste factor. Concrete is messy, forms are rarely perfect, and you do not want to stop mid-pour to run for more bags.

Example: a 12×16 foot shed foundation, 4 inches thick. 12 × 16 = 192 sq ft. 4 inches ÷ 12 = 0.333 ft. 192 × 0.333 = 64 cubic feet. 64 ÷ 27 = 2.37 cubic yards. Add 5% waste = 2.49 cubic yards. Round up to 2.5 cubic yards.

How Many Bags of Concrete in a Cubic Yard?

This is the second most common question, and the answer depends entirely on bag size:

• 80-lb bag: yields approximately 0.6 cubic feet. You need about 45 bags per cubic yard.
• 60-lb bag: yields approximately 0.45 cubic feet. You need about 60 bags per cubic yard.
• 50-lb bag: yields approximately 0.375 cubic feet. You need about 72 bags per cubic yard.
• 40-lb bag: yields approximately 0.3 cubic feet. You need about 90 bags per cubic yard.

Most home improvement stores stock 80-lb and 60-lb bags. The 80-lb bag is the better value per pound of cement, but it is heavy. If you are working alone or mixing by hand in a wheelbarrow, 60-lb bags are easier to handle.

One important note: bagged concrete is convenient, but it is labor-intensive. Mixing 45 bags by hand in a wheelbarrow is a full day of backbreaking work. For anything over 1 cubic yard, strongly consider renting a small electric mixer (about $50/day) or ordering ready-mix.

How Thick Should a Concrete Slab Be?

Thickness is not just about strength—it is about what the slab needs to support and how long it needs to last:

• Sidewalks and garden paths: 3–4 inches. No vehicle traffic, minimal load.
• Patios and shed bases: 4 inches. Standard for residential foot traffic and light storage.
• Driveways (passenger cars): 5 inches. Handles daily vehicle weight without cracking.
• Driveways (trucks / RVs): 6 inches. Required for heavier vehicles. Consider rebar reinforcement.
• Garage floors: 5–6 inches. Vehicle weight plus tool cabinets and workbenches.
• Footings for foundations: 8–12 inches thick and 16–24 inches wide. Depends on local codes and soil bearing capacity.

Always check with your local building department before pouring footings or foundation slabs. They will have specific requirements based on your soil type, frost line depth, and local seismic activity.

Concrete Cost Per Cubic Yard (2026)

Concrete prices have risen steadily over the past few years due to fuel costs and cement shortages. Here is what you can expect to pay in 2026:

• Ready-mix concrete (national average): $130–$170 per cubic yard for standard 3000 PSI mix. High-strength 4000 PSI mix adds $10–$20 per yard.
• Bagged concrete (80-lb): $5–$7 per bag. At 45 bags per yard, that is $225–$315 per cubic yard.
• Delivery fee: $50–$100 per load for ready-mix. Some suppliers waive this for orders over 5 yards.
• Short-load fee: $50–$100 extra if you order less than 3–5 cubic yards. This is why small projects often favor bagged concrete.
• Reinforcement (rebar / wire mesh): $0.50–$1.50 per square foot depending on material and spacing.
• Finishing (sealer, color, stamp): $2–$8 per square foot for decorative finishes.

The math is simple: for projects under 1 cubic yard, bagged concrete is usually cheaper because you avoid delivery and short-load fees. For projects over 1 cubic yard, ready-mix is almost always the better value.

Bagged Concrete vs. Ready-Mix: Which Should You Choose?

Choose bagged concrete when:

• Your project is under 1 cubic yard (about 45 bags of 80-lb mix)
• You have plenty of time and do not mind mixing by hand or with a small mixer
• You need to work in stages (e.g., pouring a walkway one section at a time)
• Access is tight and a concrete truck cannot reach your site
• You want to avoid delivery scheduling and minimum order requirements

Choose ready-mix concrete when:

• Your project is 1 cubic yard or larger
• You want to pour the entire project in one continuous session (critical for slabs)
• You have access for a concrete truck or pump
• You value your time and back more than the delivery fee
• You need a specific mix design (e.g., high-strength, fiber-reinforced, or colored concrete)

One hybrid option: some suppliers offer "short-load" ready-mix service with a small truck. This is perfect for 1–3 yard projects. You get the convenience of pre-mixed concrete without the massive minimum order.