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Cumulative percent retained on the 3/8 in sieve.
Cumulative means the running total including everything retained on coarser sieves above it.
Cumulative percent retained on the No. 4 sieve.
The No. 4 (4.75 mm) is the boundary between fine and coarse aggregate, so on a true concrete sand this figure should be small — a material with much retained here is a blend rather than a sand, and it will behave like one in the mix. If the number is large, check whether the sample was split correctly before the grading was run.
Cumulative percent retained on the No. 8 sieve.
The No. 8 (2.36 mm) and the No. 4 above it carry the coarse end of a sand, and together they set how harsh the mix feels under a float. A sand heavy at this end places well in a slab and fights the trowel on a finish; one that is short here is easy to finish and prone to bleeding, because there is less coarse material holding the paste in place.
Cumulative percent retained on the No. 16 sieve.
The No. 16 (1.18 mm) sits in the middle of the grading, and the middle is what makes a mix pumpable. A gap here — plenty of coarse sand and plenty of fine, with little between — gives a mix that segregates in the line and blocks at the first bend, and the grading curve will show it as a flat stretch that the fineness modulus alone cannot: two sands with the same FM can be graded quite differently.
Cumulative percent retained on the No. 30 sieve.
From the No. 30 (600 µm) downward the sand starts doing the work of a fine, filling between the larger particles and carrying paste with it. This is the region that decides water demand: a sand short of material here needs more water for the same slump, and more water is the one adjustment that costs strength.
Cumulative percent retained on the No. 50 sieve.
The No. 50 (300 µm) fraction is what a finisher feels. Concrete short of material passing this sieve bleeds, because there is nothing fine enough to hold the water, and it tears rather than closes under a power float. It is the single most common reason a technically compliant sand produces a slab nobody wants to stand behind.
Cumulative percent retained on the No. 100 sieve.
The No. 100 (150 µm) is the last sieve in the fineness modulus series, and everything passing it is counted nowhere in the number — which is exactly why FM has to be read alongside the full grading rather than instead of it. Those fines matter in both directions: too few and the mix bleeds and finishes badly, too many and water demand climbs and the paste needs more cement to hold the same strength.
Fineness modulus
2.97 (fineness modulus)
- Sum of cumulative % retained
- 297 %
They open the calculator with your figures already in it
Aggregate Fineness Modulus Calculator (ASTM C136): 2.97 (fineness modulus) — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- ASTM C136 fineness modulus: FM = (sum of cumulative percent retained on the standard sieve series: 3/8in, No.4, No.8, No.16, No.30, No.50, No.100) / 100
Inputs used
- % Retained on 3/8 in Sieve (cumulative)
- 0
- % Retained on No. 4 Sieve (cumulative)
- 5
- % Retained on No. 8 Sieve (cumulative)
- 15
- % Retained on No. 16 Sieve (cumulative)
- 35
- % Retained on No. 30 Sieve (cumulative)
- 60
- % Retained on No. 50 Sieve (cumulative)
- 85
- % Retained on No. 100 Sieve (cumulative)
- 97
Intermediate steps
- Sum of cumulative % retained
- 297 %
What this calculation does not cover
- The seven sieves here stop at 3/8 in (9.5 mm), which is enough to grade a sand. ASTM's fineness modulus series continues upward through 3/4 in, 1-1/2 in and coarser, so a coarse aggregate entered here reads low by whatever is cumulatively retained on those larger sieves — there is nowhere to enter those terms.
- Fineness modulus collapses an entire grading curve into one number. Two sands with the same value can be graded completely differently, one continuous and one gapped through the middle sieves, and this figure will not show you the gap. It also does not test ASTM C33's separate limit on how much material may be retained between two consecutive sieves.
- Nothing validates what you type. The percentages must be cumulative and must rise down the series; enter the individual retained percentages by mistake, or figures from a sample that was never split and washed to ASTM C136, and the tool sums them anyway and comments only on whether the total falls outside 2.3 to 3.1.
- The index says nothing about the rest of what makes an aggregate usable — particle shape and angularity, clay and silt content, moisture and absorption, organic impurities, soundness, or deleterious particles. A sand can sit mid-range on fineness modulus and still fail ASTM C33 on any of those.
- This is one sample on one day, not an acceptance decision and not a mix design. It does not track the source-consistency window C33 places on continuing shipments from one pit, and it does not proportion anything — selecting coarse-aggregate volume from the fineness modulus, as ACI 211.1 does, is a separate step.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- ASTM C136 fineness modulus: FM = (sum of cumulative percent retained on the standard sieve series: 3/8in, No.4, No.8, No.16, No.30, No.50, No.100) / 100
Which documents these citations point at
Standards referenced: ASTM C136 (ASTM International, United States).
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