Reading nominal rock sizes and gradation

A useful material request starts with a clear measurement, a defined use, and honest expectations about what still needs confirmation.

Decode the product label

A fraction, inch size, “minus,” “clean,” “screened,” “washed,” or local trade name may describe different grading concepts. “Minus” commonly signals material passing a top screen and can include smaller particles, but the exact distribution still needs verification. Two suppliers can use similar names for materially different blends, so ask for the defining screens or specification.

Understand a gradation

A sieve analysis reports the percentage passing a series of openings and describes the whole particle distribution. Nominal maximum size, maximum size, and a narrow screened range are not synonyms. Fines fill voids and influence compaction, drainage, dust, and tracking; open-graded material behaves differently. Use the specified test and limits when the project requires engineered performance.

Include shape and geology

Rounded, subrounded, angular, flaky, elongated, hard, soft, porous, and fractured particles can behave differently even at the same sieve size. Rock type, durability, absorption, breakage, color, and surface texture may matter for drainage, base, concrete, landscape, barefoot, or erosion uses. Do not transfer a suitability claim from one source or gradation to another.

Inspect and document the lot

Spread enough material to see the distribution and include a ruler or known scale. Photograph more than one location, note moisture and dust, and distinguish a hand-picked display from a representative sample. For specified work, request current documentation and approval before release. For decorative work, agree on the acceptable size and color range and how loads will be blended.

Before requesting pricing

Ask whether the label describes a maximum size, a passing range, an opening pair, or an informal trade name.
Record fines content, oversize allowance, angularity, wash or screen process, and applicable specification or test report.
Compare a spread, scaled current-lot sample and keep decorative appearance separate from engineered compliance.

Frequently asked questions

Does 3/4-inch rock contain only 3/4-inch pieces?

Usually not. The label may be nominal or describe a screened range. Ask for the actual gradation and current sample.

Does washed mean there are no fines?

Not necessarily. Washing method, handling, degradation, and specification affect residual fines. Verify the product rather than relying on the adjective.

Can a decorative sample prove specification compliance?

No. Engineered compliance may require source documentation, certified testing, lot traceability, and project approval in addition to visual inspection.