Concrete Calculator — Yards, Bags & Cost

How to Estimate Concrete for Any Project

Ordering concrete is a one-shot decision: order too little and you get a cold joint and a short-load fee on the second truck; order too much and you're paying $130–$190 per wasted yard. This calculator does the volume math for slabs, footings, columns, and walls, converts it to cubic yards and bag counts, and prices it with current regional ready-mix rates — including the 10% waste factor every experienced contractor builds in.

The Math Behind the Calculator

Concrete is sold by the cubic yard (27 cubic feet). For a rectangular slab, the formula is: length (ft) × width (ft) × thickness (ft) ÷ 27 = cubic yards. A 10×10 patio at 4 inches deep works out to 100 × 0.333 ÷ 27 = 1.23 yd³ — call it 1.4 yd³ after waste. Footings use the same volume math per linear foot; columns use πr²h. The calculator handles each shape and rounds to ordering increments.

Bags vs. Ready-Mix: The 0.5-Yard Rule

For small jobs, bagged concrete wins. An 80 lb bag yields about 0.60 ft³, so a cubic yard takes roughly 45 bags — at $6–$8 per bag, that's $270–$360 per yard plus your labor mixing it. Ready-mix runs $130–$190 per yard delivered, but trucks charge short-load fees ($50–$150) for orders under about 8 yards. The crossover: under half a yard, use bags; above it, price both. This calculator shows bag counts (40, 60, and 80 lb) alongside truck yardage so you can compare directly.

Regional Pricing Guide

Ready-mix prices vary more by region than by PSI rating. The national average for 3,000 PSI mix is $130–$190/yd³ delivered. The Northeast and West Coast run $160–$200; the Southeast and Midwest $120–$150. Higher-strength 4,000–5,000 PSI mixes add $10–$25/yd³. Fuel surcharges, weekend delivery, and pump truck rental (for backyard pours without truck access — $800–$1,200/day) all stack on top. Use the region selector above to localize your estimate.

Thickness, PSI, and Reinforcement — Getting the Spec Right

The right slab spec depends on the load it carries. Patios and walkways: 4 inches at 3,000 PSI with wire mesh. Driveways: 5–6 inches at 3,500–4,000 PSI with #3 or #4 rebar on a 12–18 inch grid. Garage floors: 5–6 inches at 4,000 PSI. Anything carrying trucks or equipment: 6–8 inches with engineered reinforcement. Going from 4 to 6 inches raises material cost 50% — which is exactly why you should run both thicknesses through the calculator before committing, and always check local building code minimums.

Site Prep and Pour-Day Checklist

Volume is only half the job. Before the truck arrives: excavate to depth plus 4 inches for the gravel base, compact 4 inches of crushed stone, set forms with stakes every 3–4 feet, install reinforcement on chairs (not lying on the base), and have at least two people ready — a yard of concrete weighs about 4,000 pounds and starts setting in 90 minutes. In hot weather, pour early morning; below 40°F, use cold-weather blankets or wait. The calculator's waste factor covers spillage and uneven subgrade, but it can't fix unprepared forms.

How Concrete Yardage Is Calculated

The math behind every concrete estimate is deceptively simple. Concrete is sold by the cubic yard, and one cubic yard is exactly 27 cubic feet (3 ft × 3 ft × 3 ft). The yardage formula for any rectangular shape is:

Length (ft) × Width (ft) × Thickness (ft) ÷ 27 = Cubic Yards

Let's walk through the classic DIY example: a 10×10 patio slab poured 4 inches thick.

• Convert thickness to feet: 4 inches ÷ 12 = 0.333 feet
• Find the volume in cubic feet: 10 ft × 10 ft × 0.333 ft = 33.3 ft³
• Divide by 27: 33.3 ÷ 27 = 1.23 cubic yards

So the raw order is 1.23 yd³. But you never order exactly 1.23 — the calculator adds the 10% waste factor and rounds up to the next convenient increment, which typically lands around 1.4 yd³. If you're using bagged mix, that same slab needs about 1.23 × 27 = 33.3 ft³ ÷ 0.60 ft³ per 80 lb bag = 56 bags (about 62 bags with waste). The same formula extends to other shapes: footings use the identical volume-per-linear-foot math, columns use π × radius² × height, and walls multiply the face area by the wall thickness. Get the three dimensions right and the calculator does the rest.

Waste Factor: Why You Order 10% More

Every experienced contractor builds a waste factor into their order, and the standard is 10% on top of the calculated volume. That buffer exists for three very real reasons, all of which cost real money if you ignore them.

Cold joints. Concrete starts setting in about 90 minutes. If you run short and the truck has to leave, come back, and finish the pour, the new concrete has to bond to concrete that has already begun to set. The seam that forms — the "cold joint" — is a structural weak point and an almost guaranteed crack line. A second truck also means a minimum-charge and delivery fee you weren't planning on. The 10% buffer keeps you from ever crossing that line.

Short-load fees. Ready-mix trucks have a minimum order, typically 3 to 5 yards, and often as much as 8 yards before they waive the surcharge. If you underestimate and need a top-up of half a yard, the plant charges a short-load fee of $50 to $150 for that second small delivery. You end up paying more for the wasted trip than for the concrete itself.

Overpour and surface losses. The subgrade is never perfectly level, forms flex, and you'll lose concrete to spillage, wheelbarrow residue, and screeding the excess off the surface. A rough base that's a half-inch deeper than planned across a 10×10 slab adds a full 0.15 yd³ on its own. Ordering 10% extra — and, for larger pours, ordering the truck a touch over and asking the driver to hold back the last bit so you can decide — covers all of it. The calculator's waste toggle defaults to 10% for exactly this reason.

Bags vs Ready-Mix Truck: When to Use Each

The biggest cost decision on any small project is whether to mix bags by hand or call in a ready-mix truck. The answer comes down to a breakeven point you can calculate before you order anything.

Let's price both sides. An 80 lb bag yields about 0.60 ft³ of concrete, so one cubic yard (27 ft³) takes roughly 45 bags. At $6–$8 per bag, the material alone runs $270–$360 per yard — and that's before the labor of mixing and placing 45 individual bags by hand, which is a full day of hard work. Ready-mix, by contrast, costs $130–$190 per yard delivered for standard 3,000 PSI mix, but the truck carries a short-load fee of $50–$150 for small orders under about 3 to 8 yards depending on the plant.

Here's the practical breakeven. A ready-mix minimum order is usually 1 yard. Compare a 1-yard pour: ready-mix at, say, $160/yard plus a $100 short-load fee is about $260 delivered. Bagged concrete for that same yard is 45 bags at roughly $315 in material plus a full day of mixing. So even at a single yard, the truck can win once you price your own labor. The crossover where the truck becomes unambiguously cheaper is around half a yard — below about 0.5 yd³ (roughly a 4×4 or 5×5 slab, or a handful of footings), bags make sense because the short-load fee dwarfs everything. Above 0.5 yd³, price both, but the truck almost always wins. Use the calculator to get your total yardage first, then apply this rule.

Concrete Cost Per Yard by Region

Ready-mix prices swing more by where you live than by the strength of the mix. Regional averages for standard 3,000 PSI concrete, delivered, look like this:

• Northeast: $160–$200 per cubic yard — dense urban logistics, higher fuel and labor costs, winter surcharges.
• Southeast: $120–$150 per cubic yard — abundant aggregate, mild climate, more competition among plants.
• Midwest: $120–$150 per cubic yard — plentiful limestone and sand keep raw costs low.
• West Coast: $160–$200 per cubic yard — stricter environmental rules and higher transport costs push prices up.

Three add-ons stack on top of those base rates. Strength upgrades: 4,000–5,000 PSI mixes add $10–$25 per yard. Delivery minimums: orders under 3 to 8 yards trigger $50–$150 short-load fees. Pump trucks: if the mixer can't back up to the forms, a pump adds $800–$1,200 per day. Fuel surcharges and weekend deliveries round it out. Use the region selector in the calculator above to localize your own estimate, then call two local plants and quote the exact same spec so you're comparing apples to apples.

FAQs

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

A 10×10 slab poured 4 inches thick is 1.23 cubic yards (33.3 ft³). Add the 10% waste factor and order about 1.4 yards, or roughly 56 to 62 bags of 80 lb mix.

How many 80 lb bags are in a cubic yard?

About 45 bags. Each 80 lb bag yields roughly 0.60 ft³, and 27 ft³ ÷ 0.60 = 45. Always round up and add waste for real projects.

Why do I need to order extra concrete?

To avoid cold joints and short-load fees. The subgrade is never perfectly level, forms flex, and concrete is lost to spillage and screeding. The 10% waste factor covers all of it for the cost of a few extra dollars per yard.

At what point does ready-mix beat bags?

Roughly half a cubic yard. Below that, the truck's short-load fee makes bags cheaper. Above it, ready-mix wins on both price per yard and labor, because a truck costs less per yard than 45 bags and arrives pre-mixed.

Is concrete sold by the yard the same everywhere?

No. Ready-mix is always priced per cubic yard, but the price varies by region: $160–$200 in the Northeast and West Coast, $120–$150 in the Southeast and Midwest, before short-load fees, strength upgrades, and pump charges.