Soil Particle Size Calculator

Calculator Inputs

Sample name

Input mode

Total dry mass

Specific gravity, Gs

Liquid limit, LL

Plasticity index, PI

Sieve data

Use one row per sieve: opening in mm, retained value. Use PAN for the pan row.

Report notes

Formula Used

Percent retained = retained mass ÷ total dry mass × 100.

Cumulative retained = sum of percent retained from larger sieves down to the current sieve.

Percent finer = 100 − cumulative percent retained.

D-value interpolation uses a semi-log curve: log(D) = log(D1) + [(P − P1) ÷ (P2 − P1)] × [log(D2) − log(D1)].

Uniformity coefficient Cu = D60 ÷ D10. Curvature coefficient Cc = D30² ÷ (D10 × D60).

Fractions: gravel = 100 − P4.75. Sand = P4.75 − P0.075. Fines = P0.075.

How To Use This Calculator

Enter the sample name, dry mass, and optional Atterberg limit values.
Paste sieve openings and retained masses into the data box.
Use PAN for material collected below the smallest sieve.
Press calculate to show the result above the form.
Review D10, D30, D60, Cu, Cc, fractions, and the curve.
Download the CSV file or PDF report for records.

Example Data Table

Sieve opening	Retained mass	Typical note
19 mm	30 g	Coarse gravel retained
9.5 mm	120 g	Medium gravel retained
4.75 mm	150 g	Fine gravel retained
2.0 mm	150 g	Coarse sand retained
0.425 mm	210 g	Medium sand retained
0.075 mm	160 g	Fine sand retained
Pan	80 g	Fines collected

Understanding Soil Particle Size

Soil particle size controls drainage, strength, compaction, and settlement. Engineers use gradation data to describe how much gravel, sand, silt, and clay are present. A well graded soil has many particle sizes. It can compact tightly and often carries load better. A poorly graded soil has a narrow size range. It may drain fast, but it may also ravel or settle.

Why Gradation Matters

Particle size affects field behavior from the first excavation. Coarse gravel creates open voids. Clean sand drains quickly. Fine silt may hold water and lose strength. Clay can swell, shrink, and reduce permeability. For road bases, foundations, filters, and earthworks, the particle curve helps compare soil against project limits. It also supports material acceptance during quality control.

How This Calculator Helps

This calculator converts retained sieve mass into percent retained, cumulative percent retained, and percent finer. It then estimates D10, D30, and D60 by logarithmic interpolation. These values describe the particle sizes where ten, thirty, and sixty percent of the sample is finer. They are used to compute the uniformity coefficient and curvature coefficient. The tool also estimates gravel, sand, and fines percentages.

Reading The Curve

The gradation curve plots particle size on a logarithmic axis. Percent finer is shown on the vertical axis. A smooth wide curve usually means a broad size distribution. A steep curve means the soil particles are close in size. Breaks or flat sections may show gap grading. The plotted data helps users see results faster than a table alone.

Engineering Use

Use the results as a planning and checking aid. Laboratory procedures, washing, oven drying, and sieve calibration still matter. Small weighing errors can change the fines percent. Always compare values with the project specification and the selected classification system. The calculator gives a clear engineering summary, but final design decisions should use verified test reports.

Best Input Practice

Use clean, positive masses for each sieve. Keep the pan mass with the finest fraction. The total retained mass should be close to the dry sample mass. Large loss values may show spills, trapped grains, or wet material. Repeat the test when balance errors appear during handling.

FAQs

What is soil particle size distribution?

It is the percentage split of particles by size. Engineers use it to judge drainage, compaction, filter behavior, and likely soil class.

What does percent finer mean?

Percent finer is the portion of the sample smaller than a selected sieve opening. It is also called percent passing.

What are D10, D30, and D60?

They are particle sizes where 10%, 30%, and 60% of the sample is finer. They support gradation and filter checks.

Why is Cu important?

Cu shows the spread of particle sizes. A higher value often means a wider size range, but project rules should guide acceptance.

Why is Cc important?

Cc helps identify curve shape. Values between 1 and 3 often support well graded behavior for clean coarse soils.

Can I add hydrometer data?

Yes. Add fine particle diameters in millimeters with retained or percent values. Keep the same descending size order idea.

What does mass loss mean?

Mass loss is the difference between dry sample mass and total retained mass. Large loss may show testing or handling problems.

Is the classification final?

No. It is a preliminary estimate. Final classification should use verified lab procedures, Atterberg limits, and project specifications.