Representative Size (dₚᵢ)

Representative Size (d_pi)

Problem:
If a bin holds rocks ranging from 10 mm to 20 mm, what single size should we use for calculations? Should it be 10 mm, 20 mm, or 15 mm?

Solution:
We use the geometric mean.

Representative Size:

dpi = √(Top Size × Bottom Size)

Example (10 mm to 20 mm):

d_pi = √(10 × 20) = √200 ≈ 14.14 mm

Note:
This method works best when sieve sizes are spaced relatively close together — a common spacing is a factor of √2.