Calculate Sloped Concrete Before You Order
Estimate concrete for tapered slabs, ramps, haunches, sloped strips and triangular wedge sections. Enter the finished dimensions and depths to calculate cubic feet, cubic yards, cubic meters, approximate bag counts and optional ready-mix material cost.
Choose the shape that best matches the concrete section. Results remain closed until you press Calculate.
Calculate a rectangular wedge that changes uniformly from one depth to another.
Use for a triangular prism that starts at zero thickness and increases uniformly to a maximum depth.
Enter a base thickness and the vertical rise added over the run. The tool calculates the ending depth and average thickness.
Calculate several identical tapered sections for repeated haunches, ramps, pads or transition pieces.
Automatically averages the shallow and deep ends of a uniformly tapered wedge.
See cubic feet, cubic yards and cubic meters from one calculation.
Planning counts for common 40, 60 and 80 lb bag sizes.
Enter a local ready-mix price per cubic yard for a material-only estimate.
A Concrete Wedge Calculator estimates the volume of a concrete section whose thickness changes along its length. Unlike a standard rectangular slab, a wedge is not the same depth everywhere. It may start thin and become thicker, taper from one known depth to another, or rise from zero to a full depth. Common examples include transition slabs, ramp-like placements, tapered fill, edge haunches, drainage transitions and other sloped concrete elements.
The key idea is simple: when the taper is uniform, the average depth is the midpoint between the starting and ending depths. The plan area is then multiplied by that average depth. This converts an awkward three-dimensional shape into an easy volume calculation without pretending the entire section is as thick as the deepest end.
This page is a quantity-planning tool, not a structural design tool. It does not determine the required slope, thickness, reinforcement, concrete strength, subgrade, joints, accessibility criteria, drainage or load capacity. Those project requirements should come from drawings, specifications, local rules and qualified professionals.
For a wedge with a rectangular plan that tapers uniformly from one thickness to another, first average the two depths. Then multiply the average depth by length and width.
Use consistent units. If length and width are in feet, convert inches of depth to feet before multiplying.
For a zero-to-full wedge, the starting depth is zero. That means the average depth is simply one-half of the maximum depth. The same result can also be obtained with the triangular-prism formula: one-half × base × height × width.
When maximum depth is entered in inches, divide by 12 to convert it to feet before finding cubic feet.
Select tapered, zero-to-full, slope/rise or multiple wedges.
Measure the actual finished length over which the depth changes.
Enter the average or constant width represented by the calculator mode.
Use the shallow and deep finished concrete thicknesses.
Check exact volume, extra allowance, bags and optional cost.
Suppose a concrete transition is 12 feet long and 6 feet wide. It is 2 inches thick at the shallow end and 8 inches thick at the deep end. The average depth is (2 + 8) ÷ 2 = 5 inches, or about 0.4167 foot.
The plan area is 12 × 6 = 72 square feet. Multiplying 72 square feet by 0.4167 foot gives approximately 30 cubic feet. Divide by 27 and the exact theoretical volume is about 1.11 cubic yards. If you select a 10% ordering allowance, the planning quantity becomes roughly 1.22 cubic yards before any supplier-specific rounding or minimum-order rules.
A slab may transition from one elevation or thickness to another. When the change is linear and the plan width stays constant, averaging the two depths gives the correct volume for the tapered portion.
Some ramp-like placements contain a constant base thickness plus an additional wedge created by a rise. The Slope / Rise calculator mode combines those two components by treating the ending thickness as base thickness plus rise.
Local thickening can sometimes be represented as a wedge or as a rectangular portion plus a triangular portion. If the geometry is more complex, divide it into simple solids, calculate each separately, and add the volumes.
Concrete surfaces often need planned elevations for drainage. The calculator can estimate the material quantity after the elevations and concrete thicknesses have already been established by the project design.
For identical repeated elements, use Multiple Wedges rather than manually multiplying every result. The quantity input multiplies the exact volume before the ordering allowance is applied.
| Unit | Relationship | Useful For |
|---|---|---|
| Cubic foot (ft³) | 12 × 12 × 12 inches | Small volume calculations and bag yield |
| Cubic yard (yd³) | 27 cubic feet | Ready-mix concrete ordering |
| Cubic meter (m³) | About 35.315 cubic feet | Metric specifications and comparison |
| Average depth | (Depth 1 + Depth 2) ÷ 2 | Uniform tapered wedge calculation |
| Zero-to-full average | Maximum depth ÷ 2 | Triangular wedge calculation |
Measure the run, width and both finished depths. A uniform taper uses the average of the shallow and deep ends.
A standard slab has one consistent thickness. Its volume is simply length × width × thickness. If the slab is 6 inches thick everywhere, every square foot of plan area uses the same concrete depth.
A wedge changes thickness. Using only the deepest measurement would overstate volume, while using only the shallowest measurement would understate it. A uniform linear taper uses the average depth.
The mathematical wedge volume represents ideal geometry. Real work may contain irregular excavation, subgrade variation, imperfect forms, uneven edges, spillage or dimensions that differ slightly from the plan. For that reason, contractors often plan some additional material. This calculator lets you compare 0%, 5%, 10% and 15% rather than imposing one fixed percentage.
Do not treat the selected allowance as a guarantee. Ready-mix suppliers may have order increments, truck-capacity limits, short-load fees or minimum quantities. Before placing an order, verify the required quantity with the supplier and compare the calculator result with the actual field measurements.
Small wedges, patches and transitions may be mixed from bags instead of delivered by a ready-mix truck. The calculator provides approximate counts for 40, 60 and 80 lb bags using simple planning yields. These are not manufacturer-specific promises. Actual yield varies by product, mix consistency and handling.
Always use the yield printed on the bag you plan to buy. Divide the required cubic feet, including any chosen allowance, by the manufacturer's stated yield per bag, then round up to a whole bag. For larger wedge placements, the labor required to mix many bags can become significant, so compare bagged material with ready-mix delivery.
This is the most common wedge error. If a section changes from 2 inches to 8 inches and you multiply the whole plan area by 8 inches, you are calculating a full rectangular prism rather than a taper.
If length and width are entered in feet, thickness in inches must be divided by 12. The calculator handles this conversion automatically.
The formulas on this page use plan length or horizontal run. A sloped surface length can be slightly longer. Use the dimensions that match the geometric model and project drawings.
Knowing the volume does not establish a safe thickness, reinforcement plan, ramp slope, bearing capacity or accessibility compliance. Those are design questions, not quantity conversions.
If the wedge widens or narrows as well as changes depth, one simple length × width × average-depth model may not accurately represent it. Divide the shape into smaller sections with reasonably uniform geometry.
Before concrete arrives, confirm forms, elevations, access, reinforcement or embedded items, placement equipment, finishing tools and curing materials. A tapered placement can be more sensitive to elevation control than a simple flat slab because the intended geometry depends on both the shallow and deep endpoints.
Mark the required elevations or use the control method specified for the project. Concrete placement and finishing are time-sensitive, and the shallow end of a wedge may behave differently from a deeper mass. Follow the project documents and concrete supplier recommendations for mixture selection, placement and curing.
Use related tools when your project contains more than one geometric shape. A wedge may be only one part of a larger slab, ramp, footing or concrete placement.
Estimate ordinary slabs, footings, walls and columns.
Open Concrete Calculator →Plan concrete quantity for ramp-style projects and sloped slabs.
Open Ramp Calculator →Compare slab volume when a required thickness has already been selected.
Open Slab Thickness Calculator →Estimate placement duration after the required volume is known.
Open Pour Time Calculator →Convert concrete volume into an estimated number of ready-mix loads.
Open Truck Count Calculator →Estimate reinforcement quantities when a reinforcement layout is already specified.
Open Rebar Calculator →For requirements beyond simple volume math, consult the project specifications and qualified professionals. The American Concrete Institute publishes concrete codes, standards and educational resources. For construction-worker safety topics, including silica exposure during concrete cutting and grinding, see the OSHA construction silica resources.
Good concrete quantity estimates begin with finished dimensions rather than rough visual guesses. Measure the horizontal run from the point where the taper begins to the point where it reaches the ending thickness. Then measure the width represented by that section. If the width changes substantially, split the project into two or more smaller wedges instead of forcing one average width into the calculation.
Measure both endpoint depths from the finished concrete surface to the bottom of the concrete section. If the subgrade slopes or steps independently of the top surface, a simple wedge may not capture the real shape. In that situation, break the section into rectangular and triangular components, or take several cross-section measurements and calculate each segment separately.
Plan dimensions are useful for budgeting, but formed dimensions are often better for a final order. Small differences in excavation depth can materially change volume when the wedge is wide or long. Check the shallow end, deep end and intermediate elevations before ordering ready-mix.
The calculator accepts length and width in feet and depths in inches. It converts the depth to feet internally. If you calculate manually, do not multiply feet by inches without converting the depth first.
The calculator also reports a simple depth-change slope percentage. It compares the change in concrete thickness with the horizontal run. For example, if thickness increases by 6 inches over a 12-foot run, the depth change is 0.5 foot over 12 feet, or about 4.17%. This number describes the geometry of the concrete thickness change; it is not automatically the same as the finished-surface grade, accessibility slope or drainage slope.
Average thickness is different from maximum thickness. For a 2-inch to 8-inch uniform taper, the average is 5 inches. For a zero-to-8-inch triangular wedge, the average is 4 inches. That distinction is why a wedge calculator can prevent significant over-ordering compared with treating the whole area as if it were the deepest thickness.
Not every tapered pour is a perfect triangular prism. Some sections curve, change width, contain steps, include thickened edges or transition between several elevations. The most reliable way to estimate these projects is usually to divide them into simpler shapes. Calculate a rectangular base separately, calculate each tapered wedge separately, and add the volumes together.
For a long wedge with changing width, divide the run into stations. Measure the width and depth at each station and create smaller segments. More segments generally produce a better approximation of curved or irregular geometry. For high-value or tolerance-sensitive work, use the quantity takeoff method specified by the project team rather than relying on a generic online calculator.
If the wedge surrounds pipes, drains, pits or other voids, subtract only voids that materially reduce the concrete quantity and whose dimensions are known. Small embedded items usually do not justify complicated deductions, while large blockouts can.
Concrete material cost is only one part of a wedge placement. Entering a ready-mix price per cubic yard gives a quick material-only estimate based on the selected ordering quantity. Actual invoices may include delivery charges, minimum-load or short-load fees, environmental charges, fuel surcharges, waiting time, Saturday or after-hours charges, pumping and other local costs.
Labor can also vary because tapered placements may require closer elevation control and more forming than a uniform slab. Site access, wheelbarrow distance, pump setup, reinforcement, surface finish and curing requirements can all affect total installed cost. Use the cost result as a starting point for budgeting, then obtain supplier and contractor quotes for the real project.
For small bagged-concrete wedges, compare the cost per yielded cubic foot rather than only the price per bag. A larger bag may cost more but yield more concrete. Always use the manufacturer's actual stated yield and follow its mixing instructions.
Concrete quantity is easiest to adjust before the truck is dispatched. A few minutes spent checking the wedge geometry can reduce the risk of a short load or a large leftover quantity.
Answers to common questions about tapered concrete volume and ordering.