---
title: "MIT classification system"
subject: "Soil Mechanics"
chapter: 3
key: "semester_4/soil_mechanics:mit-classification-grain-size"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/mit-classification-grain-size
site: BCT Engineering
---

# MIT classification system

Soil Mechanics · Chapter 3: Soil Identifications and Classification

- Asked in: 2079 Asoj, 3 marks; 2073 Magh, 3 marks (asked 2 times)
- Video: [MIT Soil Classification System| Percentage of Gravel, Sand, Silt and Clay](https://www.youtube.com/watch?v=NjwxcqbO8ZA) — Master Civil Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/mit-classification-grain-size
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-3

## Question

Describe the soil classification according to the MIT classification system, giving the grain size ranges of the different soil types.

## Short answer

MIT classification is a textural system based on particle size: gravel >2 mm, coarse sand 2–0.6 mm, medium sand 0.6–0.2 mm, fine sand 0.2–0.06 mm, silt 0.06–0.002 mm, clay <0.002 mm. The sand–silt boundary is 0.06 mm, differing from the International system’s 0.02 mm.

## Answer

The **MIT (Massachusetts Institute of Technology) classification** is a **textural system** that names a soil only by its **particle size**. It was proposed by Gilboy and Casagrande and later adopted by the British Standards. The soil is divided into gravel, sand, silt and clay.

| Soil type | Particle size (mm) |
|---|---|
| Gravel | > 2.0 |
| Coarse sand | 2.0 - 0.6 |
| Medium sand | 0.6 - 0.2 |
| Fine sand | 0.2 - 0.06 |
| Coarse silt | 0.06 - 0.02 |
| Medium silt | 0.02 - 0.006 |
| Fine silt | 0.006 - 0.002 |
| Clay | < 0.002 |

- The gravel-sand limit (2 mm) and the clay limit (0.002 mm) are the same as in the International (Atterberg) system, but the sand-silt boundary differs: 0.06 mm in MIT against 0.02 mm in the International system. So MIT silt (0.06 - 0.002 mm) covers a wider range than International silt (0.02 - 0.002 mm).
- A mixture is named by its major fraction, for example "silty sand" or "sandy clay".
- **Limitation:** it ignores plasticity, so soils with the same size distribution can behave very differently.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The MIT classification is based on
   A. particle size only (textural)
   B. particle size and plasticity
   C. plasticity chart
   D. origin of the deposit
   Answer: A. MIT is a textural system and ignores plasticity. (Key point: Basis of MIT system)

2. In the MIT system, clay size is
   A. less than 0.06 mm
   B. less than 0.002 mm
   C. less than 0.075 mm
   D. less than 0.02 mm
   Answer: B. Clay is < 0.002 mm; fine silt is 0.006-0.002 mm. (Key point: Clay size)

3. Gravel is larger than ... and coarse sand ranges ...
   A. 4.75 mm; 4.75-2.0 mm
   B. 2.0 mm; 2.0-0.2 mm
   C. 2.0 mm; 2.0-0.6 mm
   D. 0.6 mm; 0.6-0.06 mm
   Answer: C. MIT: gravel > 2.0 mm, coarse sand 2.0-0.6 mm. (Key point: Gravel and sand limit)

4. The main limitation of MIT classification is
   A. it cannot name gravels
   B. it uses too many field tests
   C. it needs Atterberg limits
   D. it ignores plasticity, so soils with same grading can behave differently
   Answer: D. Only size is used. (Key point: Limitation)

## Related in Soil Mechanics

- [AASHTO classification of inorganic soil](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aaashto-classify-inorganic-soil) — Soil Mechanics, chapter 3
- [Types of soil by formation, size](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Asoil-types-formation-grain-size) — Soil Mechanics, chapter 1
- [Purpose of soil classification](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Apurpose-of-soil-classification) — Soil Mechanics, chapter 3, asked 3×
- [Soil classification systems](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Acommon-classification-systems) — Soil Mechanics, chapter 3, asked 3×
- [Describe one classification system, limits](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Adescribe-classification-system-limits) — Soil Mechanics, chapter 3
- [Systems by size and plasticity; ISSCS chart](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aissc-plasticity-chart-systems) — Soil Mechanics, chapter 3

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