SI units · SI मात्रक
The 7 base units, the derived units built from them, symbols and prefixes — then test yourself in 4 games.
SI units games
What are SI units?
To measure anything, the whole world uses the same set of units — the International System of Units (SI, from the French Système International). There are 7 base units. Every other unit (like the newton or the joule) is derived from them.
The 7 base quantities
| Quantity | SI unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric current | ampere | A |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |
Common derived units
| Quantity | SI unit | Symbol | Made from |
|---|---|---|---|
| Area | square metre | m² | m × m |
| Volume | cubic metre | m³ | m × m × m |
| Speed / velocity | metre per second | m/s | distance ÷ time |
| Acceleration | metre per second squared | m/s² | change in velocity ÷ time |
| Density | kilogram per cubic metre | kg/m³ | mass ÷ volume |
| Force | newton | N | kg m/s² |
| Work / energy | joule | J | N m |
| Power | watt | W | J/s |
| Pressure | pascal | Pa | N/m² |
| Frequency | hertz | Hz | 1/s |
| Electric charge | coulomb | C | A s |
| Potential difference | volt | V | J/C |
| Resistance | ohm | Ω | V/A |
Prefixes: bigger and smaller units
| Prefix | Symbol | Means × |
|---|---|---|
| kilo | k | 1000 (10³) |
| hecto | h | 100 (10²) |
| deca | da | 10 |
| deci | d | 1/10 (10⁻¹) |
| centi | c | 1/100 (10⁻²) |
| milli | m | 1/1000 (10⁻³) |
| micro | µ | 10⁻⁶ |
| mega | M | 10⁶ |
| nano | n | 10⁻⁹ |
How to write units correctly
- Unit names start with a small letter, even when named after a person: newton, joule, kelvin (but the symbol is capital: N, J, K).
- Symbols are never made plural and take no full stop: 5 kg, not 5 kgs. or 5 Kg.
- Leave a space between the number and the symbol: 10 m, 25 °C (no space in 45° for angles).
Follows NCERT Science and Physics (Class 9 and 11). The kelvin is written without “degree”: 300 K.
A one-page chart to stick on the wall, and a worksheet to practise.
SI units
Base units
| Quantity | SI unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric current | ampere | A |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |
Derived units
| Quantity | SI unit | Symbol | Made from |
|---|---|---|---|
| Area | square metre | m² | m × m |
| Volume | cubic metre | m³ | m × m × m |
| Speed / velocity | metre per second | m/s | distance ÷ time |
| Acceleration | metre per second squared | m/s² | change in velocity ÷ time |
| Density | kilogram per cubic metre | kg/m³ | mass ÷ volume |
| Force | newton | N | kg m/s² |
| Work / energy | joule | J | N m |
| Power | watt | W | J/s |
| Pressure | pascal | Pa | N/m² |
| Frequency | hertz | Hz | 1/s |
| Electric charge | coulomb | C | A s |
| Potential difference | volt | V | J/C |
| Resistance | ohm | Ω | V/A |
Prefixes
| Prefix | Symbol | Means × |
|---|---|---|
| kilo | k | 1000 (10³) |
| hecto | h | 100 (10²) |
| deca | da | 10 |
| deci | d | 1/10 (10⁻¹) |
| centi | c | 1/100 (10⁻²) |
| milli | m | 1/1000 (10⁻³) |
| micro | µ | 10⁻⁶ |
| mega | M | 10⁶ |
| nano | n | 10⁻⁹ |
kheloaurseekho.in — free charts, games and worksheets
SI units — worksheet
Name: ____________________ Class: ______ Date: __________
1. Write the SI unit and symbol: length ________ mass ________ time ________
2. Write the SI unit and symbol: force ________ energy ________ power ________
3. Write the SI unit and symbol: pressure ________ temperature ________ current ________
4. How many base quantities are there in SI? ____ Name any four: ______________________
5. 1 km = ______ m 1 m = ______ cm 1 kg = ______ g 1 L = ______ mL
6. Correct the mistakes: 5 Kgs. → ________ 10 Newton → ________ 20 c → ________
7. The SI unit of speed is ______________ and its symbol is ______
8. Convert 25 °C into kelvin: ______________
kheloaurseekho.in — free charts, games and worksheets
