Free concrete calculator

Calculate concrete for slabs and walls

Rectangular concrete volume is the area of the face multiplied by its thickness. Use Slabs & walls for a patio, driveway panel, floor slab or rectangular wall. Enter length, width and thickness/height in the displayed units, then enter the quantity of identical pieces.

Measure and calculate

For an 18 ft × 12 ft slab that is 6 in thick, convert 6 in to 0.5 ft. Volume = 18 × 12 × 0.5 = 108 ft³ = 4 yd³ before allowance. With an illustrative 10% allowance, order-volume planning becomes 4.4 yd³. A wall uses the same geometry: length × height × wall thickness.

Separate thickened edges or beams from the uniform slab and add their extra volume without counting the slab thickness again. For wall openings, deduct only genuine voids that will not receive concrete. This volume estimate does not select a slab thickness, reinforcement or load capacity.

Calculate circular slabs and hollow concrete sections

Select Circular slabs for a round pad or annular section. The calculator asks for outer diameter, inner diameter, height/length and quantity. Set the inner diameter to zero for a solid circular slab; use the actual opening diameter for a ring or tube.

A 10 ft diameter pad has a radius of 5 ft. At 0.5 ft depth, V = π × 5² × 0.5 = 39.27 ft³, or about 1.45 yd³ before allowance. Enter 10 as the outer diameter, not 5.

For a hollow section with a 4 ft outer diameter, 2 ft inner diameter and 1 ft height, V = π × (4² − 2²) ÷ 4 × 1 = 9.42 ft³, or 0.35 yd³. The opening is a volume deduction; it must fit within the outside diameter. Do not use this mode for a tapered or irregular section without first breaking it into appropriate geometry.

Calculate square and rectangular footings

A square footing is simply a rectangle whose length equals its width. Use Slabs & walls and enter footing length, width and depth. The quantity field is useful for identical pad footings; separate rows of different sizes should be calculated independently.

A rectangular footing measuring 10 ft × 2 ft × 1.5 ft contains 30 ft³, or 1.11 yd³ before allowance. Six separate footings measuring 2 ft × 2 ft × 1 ft contain 6 × 4 = 24 ft³, or 0.89 yd³.

For intersecting strip footings, add only non-overlapping segments. Excavation overbreak, uneven ground and delivery increments can affect the order allowance. Soil capacity, footing depth, frost protection and reinforcement are design requirements; a correct cubic-volume calculation does not establish structural adequacy.

Calculate round footings, columns and post holes

Use Round footings for a solid cylinder. Enter diameter through the center, depth/height and quantity. Measuring a radius but entering it as diameter would produce only one-quarter of the intended volume because the radius is squared.

Four cylindrical footings, each 3 ft in diameter and 2 ft deep, require π × 1.5² × 2 × 4 = 56.55 ft³, or 2.09 yd³ before allowance. For different depths, calculate each group and add the volumes.

The solid-cylinder result includes the full hole. If a post or another component displaces concrete, identify that displacement separately where appropriate to the supplier and project method. Do not automatically subtract reinforcement or structural components without an agreed quantity method.

Calculate an L-shaped curb and gutter

The calculator combines two non-overlapping rectangles: the curb and the adjacent gutter flag. Enter curb depth, curb height, gutter width, flag thickness, length and quantity. Here, curb depth means the horizontal width of the curb rectangle; gutter width is the adjoining flag width, not a width that also contains the curb.

With a 6 in wide × 6 in high curb and an 18 in wide × 4 in thick gutter, the area is 0.5 × 0.5 + 1.5 × (4 ÷ 12) = 0.75 ft². Along 40 ft, volume is 30 ft³ = 1.11 yd³ before allowance.

If the curb height was measured only above the gutter surface, adjust the rectangle dimensions to match the actual non-overlapping section. For sloped, rounded or municipal standard profiles, use the approved cross-sectional area or divide the drawing into suitable shapes. A rectangular approximation is not a substitute for the specified curb detail.

Calculate solid concrete stairs with a platform

Select Stairs and enter run per step, rise per step, width, number of steps, platform depth and quantity. This calculator models a solid staircase filled down to a horizontal base, followed by a full-height solid platform. It does not model a thin suspended stair slab or a staircase filled mainly with compacted material.

Let n be the number of steps, r the rise, t the run, W the width and P the platform depth. The successive rectangular step columns have heights r, 2r, 3r and so on. Their sum is r × n(n + 1) ÷ 2.

For 4 steps, each with a 1 ft run and 0.5 ft rise, a width of 4 ft and a 3 ft platform: steps = 4 × 1 × 0.5 × 10 = 20 ft³; platform = 4 × 3 × 0.5 × 4 = 24 ft³. Total = 44 ft³ = 1.63 yd³ before allowance. Set platform depth to zero if the solid platform is absent.

Multiplying one small step block by the step count misses the concrete beneath higher treads in this solid model. Conversely, applying this full-solid formula to a hollow or sloped-underside stair overstates the quantity. Use the actual section drawing.

Convert cubic feet, cubic yards and cubic meters

Linear, square and cubic units are different. A square-foot area needs a thickness before it becomes a concrete volume. Convert all dimensions to a common unit before multiplying; 4 inches is 4 ÷ 12 feet, not 4 feet.

A 6 m × 4 m slab with a 100 mm thickness contains 6 × 4 × 0.1 = 2.4 m³. A 24 ft × 15 ft slab at 6 in contains 180 ft³, or 6.67 yd³. Retain precision in the calculation, then agree the supplier's order increment.

The allowance is applied to the quantity total once. Do not add it again to the bag count if the displayed bag result already uses adjusted volume. Uneven excavation, spillage and form tolerances differ by site; 10% is an editable example, not a structural or purchasing rule.

Understand bag yield and estimated concrete weight

Bag count should come from the volume a bag produces, not by dividing estimated wet-concrete weight by dry bag weight. Added water and product composition mean these are different quantities. This calculator uses the approximate published yields for QUIKRETE Concrete Mix No. 1101.

For 12 ft³, the 60 lb result is 12 ÷ 0.45 = 26.67, so buy at least 27 bags before any additional supplier-specific constraints. The equivalent 80 lb result is 20 bags. Always check the exact product label; lightweight, fast-setting and specialty products can have different yields.

The weight result uses a 2,130 kg/m³ estimating assumption, not a measured density or a safe vehicle load. Ask the supplier for actual mix density and comply with transport and lifting limits. Bag mass is dry packaged material; the placed-concrete estimate is not a delivery manifest.

Estimate ready-mix and site-mixed concrete costs

Start with the adjusted volume and the supplier's unit price. The calculator's cost output covers that material multiplication only. A complete job budget must include getting the concrete to the form, placing it and finishing the work.

Ready-mix example

For an illustrative 6 yd³ order at 155 per yd³, material is 930. Add delivery 95, labor 800, equipment 240 and preparation 300: total estimated job cost = 2,365 before tax and profit. The calculator shows 930 until those other costs are added in your estimate.

Site-mix example

For a planned batch whose verified yield covers the required volume, illustrative materials cost 160 for cement, 55 for sand, 45 for aggregate and 15 for water/additives: 275. Adding 120 for labor and 35 for equipment produces 430. Those numbers are cost assumptions, not a mix recipe or a claim that site mixing is cheaper for every job.

Compare like-for-like quantities and specifications, including batching effort, waste, access and finish quality. Obtain local prices; a national average cannot replace a supplier quote for your site.

Price the concrete job without confusing markup and margin

A customer's price needs to cover the complete cost basis and the return your business intends to earn. Add direct materials, labor, equipment, subcontractors and assigned overhead before applying the chosen pricing method. Keep tax separate.

At a total entered cost of 2,000, a 20% markup adds 400 and produces a 2,400 price. The margin on that cost basis is 400 ÷ 2,400 = 16.67%. A 20% target margin instead requires 2,000 ÷ 0.8 = 2,500. Use the contractor markup calculator to keep the basis visible.

State whether demolition, difficult access, unexpected ground conditions and disposal are included. A contingency included as a cost allowance is not guaranteed profit. Record approved changes separately from the original quote.

Understand concrete ingredients and mix proportions

Concrete combines a cementitious binder, fine aggregate such as sand, coarse aggregate, water and sometimes admixtures. Cement is one ingredient, not another name for the finished concrete. The required strength, exposure, workability and placement method influence the specified mixture.

What a 1:2:3 ratio means

A nominal 1:2:3 ratio describes one part cement, two parts sand and three parts coarse aggregate using a consistent stated basis. Six parts in total gives shares of 1/6, 2/6 and 3/6. It does not mean that six buckets of loose dry material produce six buckets of finished concrete, and it does not define the required water quantity.

This volume tool does not design a structural mix or guarantee M20, M30 or M40 strength. Use the approved mix specification or the packaged product instructions, including water and curing requirements. For structural work, do not convert a general ratio into a strength claim without a properly designed and verified mixture.

Prepare a clear concrete estimate

Carry the material quantity into the estimate generator, then describe the work the customer is purchasing. Separate concrete supply, preparation, reinforcement, placing, finishing and additional services where that makes the scope clearer.

• Start directly: prepare an online estimate without creating an account.
• Work on a phone: review the scope and quantities at the site.
• Download a PDF: retain a readable version to share or print.
• Use your identity: add business details, branding and terms.
• Revise before agreement: update quantities and prices, then identify the agreed version.

State delivery access, quote validity, exclusions, schedule, payment stages and the approval method. The calculator does not collect a deposit, signature or payment. Use the actual document and app features available for those steps.