Estimate concrete cubic yards, bags, ready-mix, gravel base, rebar, and project cost for common home concrete projects.
For slabs, patios, sidewalks, footings, post holes, and stairs.
Estimated concrete needed after waste
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Enter your project dimensions to estimate concrete volume, bags, ready-mix quantity, and cost.
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bags needed
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Est. total (material + tax)
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Custom or contractor quote total
May include labor, equipment, or services not reflected in Scenarios A or B. Compare carefully.
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Concrete is usually estimated by volume. For most home projects, that means multiplying the project's area by the concrete thickness, then converting the result into cubic yards, cubic feet, cubic meters, bags, or ready-mix order quantity.
This calculator handles five common project shapes: slabs and patios (rectangular), sidewalks (rectangular, measured along the centerline), strip footings (rectangular), post holes (cylinder, with optional post displacement), and stairs (stepped solid shape plus optional landing).
A small change in thickness noticeably changes the concrete needed. A 12 ft × 10 ft slab at 4 inches thick uses about 1.48 cubic yards of concrete before waste. At 5 inches thick, the same footprint uses 1.85 cubic yards — a 25% increase. The calculator shows base volume and final volume after waste so you can see how dimensions affect the result.
Bagged concrete is often used for small projects, repairs, post holes, and DIY pours where you control the pace and mixing. Ready-mix is delivered by truck and is often more practical for larger pours, but delivery fees, short-load fees, minimum order policies, and timing windows can affect the final cost and logistics.
The bag count can become physically demanding quickly. An 80 lb bag with a 0.60 cu ft yield means 45 bags per cubic yard before waste. A 10-bag project is manageable. An 80-bag project is a full day of heavy mixing. The comparison section shows both options side by side using the same project volume.
Real pours rarely match plan dimensions perfectly. Uneven subgrade, over-excavation, form variations, spillage, and finishing needs can all increase the concrete required. NRMCA CIP 31 recommends ordering more than plan dimensions to account for contingencies. The calculator lets you control the waste factor instead of hiding it, because site conditions vary.
This calculator estimates quantity and cost. It does not design concrete mixes, verify compressive strength, specify reinforcement, determine joint spacing, calculate load capacity, verify code compliance, or replace a contractor, engineer, local building department, or supplier. ACI 302.1R-15, Chapter 5 notes that slab performance depends on project-specific factors including soil support, base and subbase conditions, thickness, joint layout, reinforcement, curing, and testing — none of which this calculator evaluates.
For load-bearing slabs, structural footings, driveways, stairs, decks, foundations, retaining walls, frost-depth concerns, drainage issues, or permitted work, consult a qualified contractor, engineer, or local building department.
All volume calculations are performed in cubic feet, then converted to cubic yards and cubic meters.
Standard geometry. Applies to slab, patio, sidewalk, and strip footing modes.
Estimate-based planning assumption. Recommended per NRMCA CIP 31.
Bag yield defaults from QUIKRETE Concrete Mix Data Sheet. Always verify the yield on your specific product.
Always round up so the order is not short. Confirm minimum orders and scheduling with your supplier.
Real holes may be bell-shaped, oversize, or uneven. Displacement subtraction is approximate.
Simplified solid stair shape estimate only. Does not account for reinforcement, forms, or hollow or precast configurations.
Material quantity estimator only. Does not determine required reinforcement. Bar size context from ASTM A615/A615M.
12 ft × 10 ft patio, 4 in thick, 10% waste, 80 lb bags
Step 1 — Convert thickness: 4 in ÷ 12 = 0.333 ft
Step 2 — Base volume: 12 × 10 × 0.333 = 40.0 cu ft
Step 3 — Cubic yards: 40.0 ÷ 27 = 1.48 cu yd
Step 4 — Add 10% waste: 1.48 × 1.10 = 1.63 cu yd
Step 5 — Final cu ft: 1.63 × 27 = 44.0 cu ft
Step 6 — Bag count: 44.0 ÷ 0.60 = 73.3 → 74 bags
If using ready-mix at a 0.25 cu yd increment: 1.63 rounds up to 1.75 cu yd to order.
This calculator estimates concrete volume from project dimensions using standard geometric formulas. It converts the result to cubic feet, cubic yards, and cubic meters, applies the selected waste factor, then estimates bag count or ready-mix order quantity. Optional planning modules estimate gravel base volume, a simple rebar grid quantity, and cost categories based on user-entered prices.
This calculator provides an estimate based on the inputs you provide. It does not account for every possible material, fee, site condition, code requirement, structural requirement, labor cost, supplier policy, or professional recommendation.
These resources provide additional guidance on ordering concrete, unit conversions, and construction material management.
Related Homebase Calculators:
Before buying concrete, compare the calculator result with your project plans, supplier quote, and actual site measurements. Confirm length, width, thickness, number of holes, footing dimensions, and any base or reinforcement requirements before ordering.
The calculator is as accurate as the dimensions, waste factor, bag yield, and cost inputs you enter. It uses standard volume formulas, but real pours can vary because of uneven excavation, form movement, overdigging, spillage, and site conditions. Use the result as a planning estimate and confirm the final quantity with your supplier or contractor before ordering.
For rectangular projects, multiply length by width by thickness to get cubic feet, then divide by 27 to convert to cubic yards. If thickness is in inches, divide by 12 first to convert to feet. The calculator does this automatically and then applies your selected waste factor. For example: 12 ft × 10 ft × (4 in ÷ 12) = 40 cu ft ÷ 27 = 1.48 cu yd.
That depends on the bag yield. If an 80 lb bag yields 0.60 cubic feet, then one cubic yard requires 27 ÷ 0.60 = 45 bags before waste. A 60 lb bag at 0.45 cu ft yield requires 60 bags per cubic yard. A 40 lb bag at 0.30 cu ft yield requires 90 bags. The calculator rounds up to whole bags because partial bags are not normally purchased.
Bagged concrete may be practical for small projects, repairs, and post holes where you mix in batches at your own pace. Ready-mix may be more practical for larger pours because mixing many bags is time-consuming and physically demanding. The calculator compares both options, but delivery fees, supplier minimums, site access, timing windows, and labor can change the practical choice significantly. There is no universal answer — use the comparison to see both scenarios with your prices.
A 10% waste factor is a common planning default and aligns with NRMCA guidance on ordering more than plan dimensions to account for contingencies. The right amount depends on your project: uneven ground, irregular holes, thickened edges, and over-excavation can all increase the concrete needed. If your supplier or contractor recommends a different allowance based on site conditions, use their number.
No. This calculator estimates material quantity and cost only. It does not determine slab thickness, footing size, reinforcement requirements, load capacity, frost-depth compliance, drainage design, curing requirements, or permit needs. ACI 302.1R-15 notes that slab performance depends on many project-specific factors. For structural or permitted work, use plans from a qualified professional.
Yes. Choose the post hole mode, enter the number of holes, diameter, and depth. Optionally subtract the volume displaced by a round or square post by enabling post displacement and entering the post dimensions and embedded depth. Real holes may use more concrete if they are uneven, oversize, or bell-shaped at the bottom. The displacement calculation is approximate.
Yes. The Advanced Options panel includes a simple rebar grid quantity estimator for slabs, patios, and sidewalks. Enter bar spacing, stick length, lap and waste factor, and price per stick to estimate linear feet, stick count, and cost. This estimates material quantity only — it does not determine whether reinforcement is required, what bar size is appropriate, or whether the layout meets code. See ASTM A615/A615M for bar specification context.
Ready-mix is ordered in volume increments set by the supplier — commonly 0.25 cubic yard increments. The calculator always rounds up so the order is not short of the final volume after waste. For example, 1.63 cubic yards rounds up to 1.75 cubic yards at a 0.25 increment. Confirm minimum orders, delivery fees, short-load policies, and scheduling requirements directly with your supplier before placing an order.
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