The Fineness Modulus Calculator helps engineers, construction managers, and materials testing professionals quickly determine the fineness modulus (FM) of aggregate samples. FM is a key index number that represents the mean particle size of a sample. It is used widely in concrete mix design, asphalt mix design, and quality control of aggregates. This calculator simplifies the tedious manual process by adding up cumulative percent retained values on standard sieves and computing the final modulus instantly.
This tool belongs in the Construction Materials Testing and Aggregate Analysis category.
Formula of Fineness Modulus Calculator
Fineness Modulus (FM) = (Sum of Cumulative Percent Retained on Standard Sieves) / 100
Where:
- Cumulative Percent Retained: The total percentage of material retained on each specified standard sieve.
- Standard Sieves: Typically a series such as 150 µm (No. 100), 300 µm (No. 50), 600 µm (No. 30), 1.18 mm (No. 16), 2.36 mm (No. 8), 4.75 mm (No. 4), 9.5 mm, 19 mm, and so on.
For example, after a sieve analysis, you add the cumulative percentages retained on each sieve and divide by 100 to get the FM.
Typical FM Ranges Table
| Material Type | Common FM Range |
|---|---|
| Fine Sand | 2.2 – 2.6 |
| Coarse Sand | 2.6 – 2.9 |
| Gravel (coarse aggregate) | 6.0 – 7.0 |
| All-in Aggregate | 4.7 – 5.6 |
This table helps users estimate suitable FM ranges for different aggregate types used in concrete or asphalt.
Example of Fineness Modulus Calculator
Suppose a sieve analysis of sand yields the following cumulative percent retained:
- No. 4: 5%
- No. 8: 20%
- No. 16: 45%
- No. 30: 70%
- No. 50: 90%
- No. 100: 97%
Sum of cumulative percent retained: 5 + 20 + 45 + 70 + 90 + 97 = 327
Then,
Fineness Modulus = 327 / 100 = 3.27
So, the FM of this sand sample is 3.27.
Most Common FAQs
For concrete sand, an FM between 2.3 and 3.1 is typical. Finer sand lowers the FM; coarser sand raises it. Always follow project specifications for optimal results.
FM affects workability, strength, and economy of concrete mixes. A higher FM means coarser aggregate, which usually reduces the need for cement paste but might lower workability if not properly adjusted.
No. FM is a helpful indicator but should be combined with other tests like gradation curves, specific gravity, and absorption to fully understand an aggregate’s properties.