Fineness Modulus
Single index of aggregate coarseness from cumulative sieve retention
The fineness modulus (FM) is an empirical single-number index of an aggregate's average particle size, computed as the sum of the cumulative percentages retained on the standard IS sieves divided by 100 (IS 2386 Part 1 sieve analysis). A higher FM means a coarser aggregate. Typical FM ranges: fine sand 2.2-2.6, medium sand 2.6-2.9, coarse sand 2.9-3.2; for coarse aggregate FM is much higher (6.5-8).
FM is used to classify sand into grading zones (IS 383 Zones I-IV), to proportion fine-to-coarse aggregate in mix design (IS 10262), and to monitor consistency of incoming material. Two sands with the same FM can still have different gradings, so FM is used alongside the full sieve curve, not instead of it. A sudden FM shift in deliveries signals a changed source and triggers a mix-water/admixture re-check.
- Sand grading-zone classification (IS 383 Zones I-IV)
- Concrete mix proportioning (IS 10262)
- Incoming-aggregate consistency control
- Mortar + plaster sand selection
- Detecting source change in deliveries