Concrete Wedge Calculator 2026 - Volume, Bags & Cost for Tapered Slabs

The standard wedge volume formula is V = (b x h / 6) x (2a + c), where b = width, h = height (rise), a = base length, and c = top length. For the most common field case (tapered slab with flat top and flat bottom), the simpler average-thickness formula is identical: V = ((thick end + thin end) / 2) x length x width / 27. When the top tapers to zero, use the triangular prism formula: V = (length x width x thick-end depth) / 2 / 27.

Concrete wedges appear in many field applications: loading dock approach ramps that transition from yard elevation to dock height, driveway and garage apron transitions at existing pavement joints, floor leveling pads under machinery on uneven slabs, bridge approach wedges to smooth the stiffness change between rigid and flexible pavement, and drainage-sloped pads around building foundations. Any pour that is thicker on one end than the other is a wedge shape. For stairs and stepped transitions, see our concrete staircase calculator.

A standard 12-foot-wide dock approach that transitions from 4 inches at the yard to 10 inches at the dock over a 20-foot run requires approximately 4.4-5.0 cubic yards (with 10% waste). A 16-foot-wide approach over the same run is roughly 5.9-6.5 cubic yards. Most dock approach wedges fall in the 3-8 cubic yard range, making them good candidates for a single ready-mix truck. Calculate your exact yardage with our concrete cubic yard calculator.

Minimum PSI depends on use: residential pedestrian transitions use 3,000 PSI, driveway and light vehicle use 3,500-4,000 PSI, loading dock and heavy vehicle use 4,000-4,500 PSI, and industrial/bridge approach wedges require 4,500-5,000 PSI per ACI 318. The thin feathered edge is structurally weaker than the thick end - using higher PSI concrete is inexpensive insurance against early edge cracking. Verify requirements with our PSI strength calculator.

Yes, for any wedge under vehicle loads. ACI 302.1R requires reinforcement for all commercial slabs under wheeled traffic. Use #4 rebar on 18-inch centers for light vehicles, #4 on 12-inch centers for loading docks, and #5 on 12-inch centers for industrial fork truck traffic. Stop rebar bars 2 inches from the feathered edge where the slab is too thin to maintain cover. Wire mesh (6x6 W2.9) is acceptable for pedestrian-only transitions and leveling pads with no vehicle traffic.

Yes, for small wedges under 1 cubic yard (27 cubic feet). An 80 lb bag yields 0.60 cubic feet, so a small garage apron wedge of 15 cubic feet needs 25 bags. For wedges over 1 cubic yard, ready-mix is more cost-effective - bagged concrete for 2+ yards means 90+ 80 lb bags, which is physically exhausting and adds significant labor time. Ready-mix also gives you better control over the pour rate, which is important for properly filling a tapered form. See our yardage calculator to decide.

Four practices reduce thin-edge cracking: (1) Never feather below 4 inches under vehicle loads - the absolute minimum for any traffic is 3 inches. (2) Use 4,000 PSI minimum throughout. (3) Moist-cure the thin end aggressively - apply curing compound or wet burlap within 20 minutes of finishing. The thin end dries 3x faster than the thick end. (4) Apply a bonding agent at the thin-end joint if tying into existing concrete. For structural load analysis of your slab, see our load bearing calculator.

The slope angle is calculated as: angle = arctan((thick end - thin end) / (length x 12)). For example, a wedge that goes from 8 inches to 4 inches over 10 feet has a rise of 4 inches over 120 inches = 3.3% slope (about 1.9 degrees). ADA maximum ramp slope is 8.33% (1:12). Typical loading dock approaches run 10-15%. The calculator displays slope automatically once you enter dimensions. For ADA-compliant ramp design, use our dedicated concrete ramp calculator.