Concrete quantity toolsConcrete quantities
Tapered slab volume
Estimate concrete for a slab whose thickness changes at a constant rate from one end to the other.
Enter your measurements
How it is calculated
V = length × width × (start thickness + end thickness) / 2.
Keep the full result when using it in another calculation. Results show up to three decimal places; very small positive results use scientific notation (for example, 1e-6). No extra material for waste is added.
Measure the endpoints of the taper
Use the horizontal plan length and the constant width of the slab. Measure thickness perpendicular to the slab’s reference plane at each end. The model assumes thickness changes steadily from the start value to the end value.
If one end tapers to a point, enter zero for that end. If a slab has separate flat and tapered sections, calculate the sections separately so each region follows its own geometry.
Use the average endpoint thickness
For a 10 ft by 4 ft slab that changes linearly from 0 ft thick to 1 ft thick, the average thickness is (0 + 1) ÷ 2 = 0.5 ft. The volume is 10 × 4 × 0.5 = 20 ft³.
The average of the two end thicknesses works because the change is linear. It does not establish a reliable volume for an irregular surface by itself; isolated depth readings may not capture the shape between measurement points.
Before you use the result
- The slab width must stay the same. Thickness must increase or decrease at a constant rate along its length.
- Use horizontal plan length, not the length of the sloped surface. Measure thickness perpendicular to the slab’s reference plane. Averaging scattered depth readings does not give a reliable result for an irregular slab.