Concrete Order Calculator: How Much to Order

A concrete order calculator works out the volume of ready-mix concrete you need for a slab, footing, or other pour, based on the dimensions you enter. You input the length, width, and thickness (or the diameter and depth for a round column), and it returns the volume in cubic yards or cubic meters, plus an estimate of how many bags of pre-mix concrete to buy. This page gives you the calculator, the formulas behind it, and practical guidance on ordering so you don’t end up short or with a truckload of leftover concrete.

Formula

The core formula for a rectangular slab is:

Volume (cubic feet) = Length (ft) × Width (ft) × Thickness (ft)

Because thickness is usually given in inches, convert it to feet first: Thickness (ft) = Thickness (in) ÷ 12. Then convert cubic feet to cubic yards, the standard unit for ready-mix orders: Cubic yards = Cubic feet ÷ 27 (since 1 yard = 3 feet, so 1 yd³ = 27 ft³).

For a round column or footing, use the cylinder formula: Volume (ft³) = π × (Diameter/2)² × Height (ft), then divide by 27 for cubic yards. The calculator above uses the rectangular formula, but the same conversion applies.

Worked Example

Using the default values from the calculator: a slab that is 10 ft long, 10 ft wide, and 4 inches thick.

1. Convert thickness to feet: 4 in ÷ 12 = 0.333 ft
2. Calculate cubic feet: 10 × 10 × 0.333 = 33.3 ft³
3. Convert to cubic yards: 33.3 ÷ 27 = 1.23 yd³
4. For 60-lb bags (each yields about 0.45 ft³): 33.3 ÷ 0.45 = 74 bags (rounded up)

The calculator shows 1.23 cubic yards, 33.33 cubic feet, and 74 bags. That matches the step-by-step result.

How to Use the Calculator

Enter the length and width in feet (or meters if you prefer, but be consistent). Enter the thickness in inches for a slab. The calculator gives you three outputs:

• Cubic yards – the number you give to a ready-mix supplier.
• Cubic feet – useful for small pours or bag calculations.
• Number of 60-lb bags – for DIY projects where you mix bags yourself.

For a round column, you would need a different calculator, but the same principle applies: compute the volume in cubic feet, then divide by 27.

Ordering Ready-Mix: What You Need to Know

Ready-mix concrete is sold by the cubic yard. Most suppliers have a minimum order (often 1 cubic yard) and charge extra for partial loads. When you order, you’ll need to specify:

• The total volume in cubic yards (round up to the nearest quarter or half yard).
• The strength (e.g., 3000 or 4000 psi) – your engineer or local code may specify this.
• Whether you need admixtures (e.g., air entrainment for freeze-thaw climates, accelerators for cold weather).

Always order a little extra – typically 10% more – to account for uneven subgrade, spillage, or variations in form dimensions. For a 1.23 yd³ pour, that means ordering about 1.4 yd³.

Common Mistakes and How to Avoid Them

Several errors trip up DIYers and even pros:

• Mixing units: Don’t multiply feet by inches. Convert everything to feet first.
• Forgetting the thickness conversion: A 4-inch slab is 0.333 ft, not 0.4 ft.
• Underestimating waste: The ground is rarely perfectly level, and forms can bulge. Add 10% to your final volume.
• Ignoring the minimum order: If you need 0.8 yd³, the supplier may still charge for a full yard.
• Rounding too early: Keep full precision in your calculations, then round up at the end.

For bagged concrete, each 60-lb bag yields about 0.45 ft³, and an 80-lb bag yields about 0.6 ft³. Always round up to the nearest whole bag.

Cost Considerations

Concrete prices vary widely by region, supplier, and strength. As a rough guide, ready-mix costs between $100 and $150 per cubic yard (as of 2024), but that’s just the material – delivery fees, minimums, and taxes add more. Bagged concrete is more expensive per cubic foot, but you avoid delivery fees and can mix only what you need. For a 1.23 yd³ pour, you’d need about 74 bags of 60-lb mix, which might cost $4–$6 per bag, totaling $300–$450. Ready-mix would be around $150–$200 plus delivery, so for this size, ready-mix is usually cheaper if you can handle the logistics.

Note that prices change and vary; always get a quote from local suppliers.

Safety and Practical Tips

Concrete work involves heavy materials and wet cement, which can cause skin burns. Wear gloves, long sleeves, and eye protection. When pouring, keep the concrete moving to avoid cold joints. If you’re ordering ready-mix, have your forms, reinforcement, and tools ready before the truck arrives – concrete sets quickly, and you can’t pause the pour. For large slabs, consider hiring a crew or at least having friends help with screeding and finishing.

Also, check local building codes for minimum slab thickness and reinforcement requirements. A 4-inch slab is typical for patios and walkways, but driveways often need 5–6 inches with rebar or wire mesh.

Alternatives to Ready-Mix

For small projects, bagged concrete is the obvious alternative. For very large projects, you might consider a volumetric mixer truck, which mixes on-site and lets you order exact amounts. For non-structural uses, you could use pre-cast blocks or pavers, which require no pouring at all. But for most slabs and footings, ready-mix is the standard.

Frequently Asked Questions

How much concrete do I need for a 10×10 slab?

For a 10 ft × 10 ft slab at 4 inches thick, you need 1.23 cubic yards (about 33.3 cubic feet). That’s roughly 74 60-lb bags or 56 80-lb bags. If you’re ordering ready-mix, round up to 1.5 yards to account for waste.

How many 80-lb bags are in a cubic yard?

An 80-lb bag yields about 0.6 cubic feet. One cubic yard is 27 cubic feet, so you need 27 ÷ 0.6 = 45 bags. For a 60-lb bag (0.45 ft³), you need 60 bags per cubic yard.

What is the difference between a cubic yard and a cubic meter?

A cubic yard is 27 cubic feet, while a cubic meter is about 35.3 cubic feet. One cubic yard equals 0.7646 cubic meters. Ready-mix in the US is sold by the cubic yard; in most other countries, it’s sold by the cubic meter.

Should I order extra concrete?

Yes, it’s standard practice to order 10% more than the calculated volume. This covers uneven subgrade, form expansion, spillage, and slight over-excavation. If you don’t use it, you can’t return it, but being short is worse – a cold joint weakens the slab.

How do I calculate concrete for a round column?

Use the cylinder formula: Volume = π × (diameter/2)² × height. For a 1-ft diameter column that’s 4 ft tall: π × (0.5)² × 4 = 3.14 ft³, or about 0.12 yd³. Convert to bags using 0.45 ft³ per 60-lb bag.

Can I use this calculator for a footing?

Yes, if the footing is rectangular. Enter the length, width, and thickness (depth) of the footing. For stepped or trapezoidal footings, break them into rectangular sections and add the volumes together.

Related

• Drywall Repair Calculator: Estimate Material & Cost
• Drywall Mud Calculator: How Much Joint Compound
• Drywall Needs Calculator: How Much Do You Need?

in l | Length | ft | 10 | 0
in w | Width | ft | 10 | 0
in d | Thickness | in | 4 | 0
out cy | Cubic yards | yd³ | l * w * (d / 12) / 27 | 2
out cf | Cubic feet | ft³ | l * w * (d / 12) | 2
out bags | 60-lb bags | bags | ceil((l * w * (d / 12)) / 0.45) | 0