Calculate Concrete For Triangular Pads, Slabs, Islands & Wedges
Use this Triangular Concrete Calculator to estimate concrete volume for triangular slabs, pads, wedges and prisms. Calculate triangle area from base × height or all three sides, multiply by concrete thickness or prism length, then convert the result into cubic feet, cubic yards, cubic meters, concrete bags and optional material cost.
Calculate triangle slabs, three-side triangles, triangular prisms/wedges, or multiple sections.
Calculate a triangular pad, slab or concrete island from base, perpendicular height and thickness.
Uses a constant slab thickness across the triangular plan area. Thickened edges or beams should be calculated separately.
Use all three triangle side lengths to find area with Heron’s formula, then multiply by slab thickness.
The three side lengths must satisfy the triangle inequality.
Calculate a triangular cross-section and extend it along a length for wedges, ramps and tapered sections.
Assumes a constant triangular cross-section for the full entered length.
Add up to three triangular slab sections with base, perpendicular height and thickness.
Use separate sections when thickness changes. Curves, haunches and thickened edges should be calculated separately.
A Triangular Concrete Calculator estimates concrete volume when the plan shape or cross-section of the concrete is triangular. Typical examples include triangular patio corners, driveway infill sections, traffic islands, landscape pads, ramp wedges, tapered concrete fills and triangular sitework details.
A rectangular slab calculator uses length × width × depth. A triangle changes only the area portion of the equation. If you know the triangle base and the perpendicular height, the area is one-half of base × height. Multiply that area by concrete thickness to obtain volume.
If the perpendicular height is difficult to measure but all three side lengths are known, Heron’s formula provides another way to determine triangle area. That makes the three-side mode especially useful for irregular field measurements.
Calculate triangular pads and slabs from base, perpendicular height and thickness.
Use Heron’s formula when all three sides are known but the altitude is not.
Extend a triangular cross-section along a length for tapered concrete shapes.
Convert total volume into 40, 60 and 80 lb bag estimates or optional ready-mix cost.
First identify whether the triangle exists in plan view or in cross-section. A triangular patio corner is a plan-view triangle with a constant slab thickness. A concrete wedge or simple ramp transition may have a triangular side profile that continues for a fixed length. Choosing the correct orientation prevents using the right formula on the wrong dimensions.
Decide whether the triangle is the slab footprint or the wedge cross-section.
Use one side as the triangle base.
Measure perpendicular to the selected base.
For slab mode, enter the concrete thickness in inches.
Check yd³, ft³, m³, bags, allowance and cost.
For a triangular slab with constant thickness, calculate triangle area first and multiply by slab depth.
Base and perpendicular height must use the same unit.
If base and height are in feet, convert thickness from inches to feet before multiplying.
One cubic yard contains 27 cubic feet.
If a triangular concrete patch is irregular, measuring the perpendicular height can be awkward. When all three side lengths are known, Heron’s formula can calculate the plan area without directly measuring an altitude.
The value s is the semiperimeter.
The three side lengths must form a valid triangle.
After area is known, multiply it by slab thickness. The calculator also checks the triangle inequality and rejects side combinations that cannot form a triangle.
A triangular prism has a constant triangular cross-section extended along a straight length. In concrete work, this can represent a simple wedge, tapered infill strip, ramp transition or triangular haunch when the cross-section remains constant.
Keep dimensions in feet for cubic feet or meters for cubic meters.
If both width and height change along the length, the shape is not a simple triangular prism and should be divided into smaller solids or calculated with a more appropriate geometry method.
The height used in the triangle area formula is not automatically one of the sloping sides. It is the shortest right-angle distance from the chosen base line to the opposite vertex. For a right triangle, one leg may be used as the base and the other perpendicular leg as the height.
For an irregular or oblique triangle, the perpendicular height may be difficult to lay out in the field. In that case, measure all three sides carefully and use the 3-Side Triangle mode instead.
Triangular sections often appear where a rectangular slab meets an angled boundary, walkway, curb or landscape feature. Estimating that triangle as a full rectangle overstates concrete quantity, while ignoring it understates the order. Calculating the triangular section separately produces a cleaner takeoff.
For example, a triangle with a 12 ft base and 10 ft perpendicular height has 60 ft² of plan area. At 4 inches thick, exact concrete volume is 20 ft³, or about 0.74 yd³ before allowance.
If the project also contains rectangular concrete, calculate those areas with the Concrete Calculator and add the triangular volume once.
A simple ramp or tapered infill that rises linearly from zero thickness to a maximum thickness creates a triangular cross-section. If that cross-section continues for a constant width or length, it can be treated as a triangular prism.
Some real ramps do not start at zero thickness. A ramp that is 4 inches thick at the low end and 12 inches thick at the high end should be treated as a 4-inch rectangular base plus an additional 8-inch triangular wedge, rather than as a zero-to-12-inch triangle.
For specialized slope calculations, use the Concrete Ramp Calculator where appropriate.
Small triangular pads and patches are often mixed from bagged concrete. The calculator uses approximate planning yields of 0.30 ft³ for a 40 lb bag, 0.45 ft³ for a 60 lb bag and 0.60 ft³ for an 80 lb bag.
| Bag Size | Planning Yield | Approx. Bags per 1 ft³ | Reminder |
|---|---|---|---|
| 40 lb | 0.30 ft³ | 3.34 | Verify actual product yield |
| 60 lb | 0.45 ft³ | 2.23 | Verify actual product yield |
| 80 lb | 0.60 ft³ | 1.67 | Verify actual product yield |
Bag yield varies by manufacturer and product, so final purchasing should follow the yield printed on the bag you actually buy.
Exact geometric volume assumes perfect forms, perfect measurements and a uniform base. Real construction may use more concrete because of uneven subgrade, small form movement, spillage, pump loss, over-excavation or slightly larger field dimensions.
The calculator includes an editable allowance instead of forcing one universal percentage. Use project history and actual site conditions to decide what is appropriate.
Suppose a triangular slab has a 15 ft base, an 8 ft perpendicular height and a 5 in thickness. Triangle area is ½ × 15 × 8 = 60 ft². Five inches equals 0.4167 ft. Multiplying 60 × 0.4167 gives about 25 ft³ of concrete, or approximately 0.93 yd³ before allowance.
With a 10% allowance, planned volume is about 27.5 ft³, or approximately 1.02 yd³. The same quantity is about 0.78 m³.
For concrete industry education and technical resources, visit the American Concrete Institute (ACI) and the National Ready Mixed Concrete Association (NRMCA). Use project drawings, specifications, local requirements and supplier information for final design and ordering.
The key measurement is the perpendicular height from the selected base to the opposite vertex.
Base: any side can be chosen as the base.
Perpendicular height: measure at 90° from the base to the opposite corner.
Thickness: slab depth is separate from the triangle’s plan height.
Volume: ½ × base × height × thickness.
Common questions about triangle area, slab volume, wedges, three-side triangles and concrete ordering.