How to Read a Sieve Analysis

From retained weights to a percent-passing curve and the fineness modulus

BuildFactor EditorialAugust 28, 20261 min read

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What the test measures

A sieve analysis (commonly run to a standard such as ASTM C136 for aggregates) shakes a weighed sample through a stack of sieves with progressively smaller openings, then weighs how much material is retained on each sieve. This shows the particle-size distribution — how much of the sample is coarse versus fine.

From retained weight to percent passing

For each sieve, cumulative retained weight (the running total retained on that sieve and all coarser sieves above it) is divided by the total sample weight and expressed as a percentage. Percent passing is 100% minus cumulative percent retained — it tells you what fraction of the sample is finer than that sieve's opening size.

The fineness modulus

The fineness modulus is calculated by summing the cumulative percent retained on a specific standard set of sieves and dividing by 100. It's a single number used to characterize how coarse or fine an aggregate is overall — a higher fineness modulus indicates a coarser gradation. It's commonly used for fine aggregate (sand) grading in concrete mix design.

Checking for a well-graded material

A well-graded aggregate has a reasonably smooth distribution across sieve sizes rather than being concentrated in just one or two sizes (gap-graded) — this typically produces better compaction and strength characteristics for most base and concrete applications. Specification limits (an upper and lower percent-passing bound per sieve) are set by the project or applicable standard and should be checked against, not assumed.

Worked Example

500 g sample; 120 g retained on a sieve, with 200 g retained on all coarser sieves above it.

Cumulative retained on this sieve: 200 + 120 = 320 g

Cumulative % retained: 320 ÷ 500 × 100 = 64%

% passing this sieve: 100 − 64 = 36%

Assumptions & Limitations

A small discrepancy between total retained weight and original sample weight (a shortfall of a percent or two) is normal and reflects material lost as dust or fines finer than the last sieve.