SCIENCE IMPORTANT FORMULAE CLASS - 9
Important Formulae for class 9 science
Updated for new syllabus - 2026
Class 9 science Important Formulae
The Important Science Formulae section at Saraswat Academy provides a complete collection of chapter-wise scientific formulas based on the latest CBSE Syllabus 2026–27. These formulas are carefully selected from the NCERT textbooks and presented in a simple, easy-to-understand format for quick learning and revision. They help students strengthen their conceptual understanding, solve numerical problems accurately, and improve problem-solving speed in Physics, Chemistry, and other formula-based topics. Regular practice of these formulas is essential for homework, class tests, unit tests, practical examinations, half-yearly examinations, annual examinations, and CBSE board examinations. This page serves as a quick revision resource, enabling students to recall important formulas confidently and perform better in both school and competitive examinations.
Regular revision of scientific formulas helps students strengthen conceptual understanding, improve numerical problem-solving skills, and reduce errors in calculations during examinations. Whether you are preparing for school assessments, practical examinations, or CBSE board exams, these chapter-wise science formula sheets provide a quick and effective revision resource. Students are encouraged to practise these formulas alongside NCERT questions, exemplar problems, practical-based questions, competency-based questions, and previous years' board questions to develop scientific reasoning, enhance accuracy, and achieve excellent marks in Science.
Important Formulae: Science Class - 9
Chapter -2
Important Formulae - Chapter 2: Cell - The Building Block of Life
1. Formula to Estimate the Size of a Cell
Estimated Size of Cell
Estimated Size of Cell = Diameter of Visible Field (in µm) ÷ Number of Cells Along the Diameter
Formula:
Estimated Size of Cell = Visible Field Diameter (µm) / Number of Cells
Example
- Diameter of visible field = 5000 µm
- Number of onion cells = 25
Estimated Cell Size = 5000 ÷ 25 = 200 µm
2. Total Magnification of a Microscope
Formula
Total Magnification = Eyepiece Magnification × Objective Lens Magnification
Example
- Eyepiece = 10X
- Objective Lens = 10X
Total Magnification = 10 × 10 = 100X
3. Unit Conversion
| Conversion | Value |
|---|---|
| 1 millimetre (mm) | 1000 micrometres (µm) |
| 1 nanometre (nm) | 0.000001 mm |
| 1 metre (m) | 1,000,000,000 nanometres (nm) |
4. Human Eye Resolution
| Quantity | Value |
|---|---|
| Limit of Resolution of Human Eye | 0.1 mm |
| Normal Viewing Distance (Near Point) | 25 cm |
5. Typical Cell Size
| Cell Type | Typical Size |
|---|---|
| Prokaryotic Cell | 1–10 µm |
| Eukaryotic Cell | 10–100 µm |
| Cell Membrane Thickness | 7–10 nm |
6. Important Numerical Values
| Quantity | Value |
|---|---|
| Robert Hooke's Microscope Magnification | 200–300X |
| Common School Microscope Objective Lens | 10X, 40X |
| Large Plant Vacuole | Usually One Central Vacuole |
| Average Lifespan of Human RBC | 120 Days |
| Cells Replaced in Human Body Daily | Hundreds of Billions (≈1% of Total Cells) |
Important Exam Formulae (Quick Revision)
- Estimated Cell Size = Visible Field Diameter (µm) ÷ Number of Cells
- Total Magnification = Eyepiece × Objective Lens
- 1 mm = 1000 µm
- 1 nm = 0.000001 mm
- Human Eye Resolution = 0.1 mm
- Cell Membrane Thickness = 7–10 nm
- Prokaryotic Cell Size = 1–10 µm
- Eukaryotic Cell Size = 10–100 µm