Written by IGCSEPhysics Content Team · Physics subject adviser: K. S. Tan, 15+ years teaching IGCSE Physics · Checked against the Cambridge IGCSE Physics (0625) 2026 to 2028 syllabus
This page lists every unit you need for Cambridge IGCSE Physics 0625, organised by quantity.
Base SI units
These are the fundamental units from which all other units are derived.
| Quantity | Unit name | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric current | ampere | A |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
Derived SI units in IGCSE Physics
These units are combinations of base units.
| Quantity | Unit name | Symbol | In base units |
|---|---|---|---|
| Force | newton | N | kg m/s^2 |
| Energy / Work | joule | J | kg m^2/s^2 |
| Power | watt | W | kg m^2/s^3 (= J/s) |
| Pressure | pascal | Pa | kg/(m s^2) (= N/m^2) |
| Frequency | hertz | Hz | 1/s |
| Electric charge | coulomb | C | A s |
| Potential difference | volt | V | kg m^2/(A s^3) (= J/C) |
| Resistance | ohm | ohm | kg m^2/(A^2 s^3) (= V/A) |
| Speed / Velocity | (no special name) | m/s | m/s |
| Acceleration | (no special name) | m/s^2 | m/s^2 |
| Density | (no special name) | kg/m^3 | kg/m^3 |
| Specific heat capacity | (no special name) | J/(kg K) | m^2/(s^2 K) |
| Specific latent heat | (no special name) | J/kg | m^2/s^2 |
SI prefixes
| Prefix | Symbol | Multiplier | Example |
|---|---|---|---|
| mega | M | 1 000 000 (10^6) | 1 MW = 1 000 000 W |
| kilo | k | 1 000 (10^3) | 1 km = 1 000 m |
| (base) | - | 1 | 1 m |
| centi | c | 0.01 (10^-2) | 1 cm = 0.01 m |
| milli | m | 0.001 (10^-3) | 1 mA = 0.001 A |
| micro | mu | 0.000001 (10^-6) | 1 micro F = 0.000001 F |
| nano | n | 10^-9 | 1 nm = 10^-9 m |
Unit conversions commonly tested
Length
- 1 km = 1 000 m
- 1 m = 100 cm = 1 000 mm
- 1 cm = 0.01 m
Mass
- 1 kg = 1 000 g
- 1 g = 0.001 kg
- 1 tonne = 1 000 kg
Time
- 1 minute = 60 s
- 1 hour = 3 600 s
Area and Volume
- 1 m^2 = 10 000 cm^2
- 1 m^3 = 1 000 000 cm^3
- 1 litre = 1 000 cm^3 = 0.001 m^3
Temperature
- T(K) = T(degrees C) + 273
- 0 degrees C = 273 K
- 100 degrees C = 373 K
Electrical
- 1 kV = 1 000 V
- 1 mA = 0.001 A
- 1 kW = 1 000 W
- 1 kWh = 3 600 000 J
How to check your unit in a calculation
After calculating, verify the unit makes sense:
- If you calculated speed, the unit should be m/s (not m or s).
- If you calculated energy, the unit should be J (not W or N).
- If you converted units in the calculation, the final unit should reflect the conversion.
The “unit mark” in exams
In most IGCSE Physics calculation questions, 1 mark is specifically for the correct unit. This is a straightforward mark to earn and a frequent one to lose. Always write the unit.
Frequently Asked Questions
What does SI stand for?
SI stands for Systeme International d'Unites (International System of Units). It is the internationally agreed system of measurement used in science.
Do I need to memorise all SI units?
You need to know the base units (metre, kilogram, second, ampere, kelvin, mole) and the derived units used in the IGCSE Physics syllabus. The exam will not ask you to define the SI system, but every calculation answer must include the correct unit.
What are SI prefixes?
Prefixes modify the size of a unit. Kilo (k) means 1000, mega (M) means 1 000 000, milli (m) means 0.001 and micro (mu) means 0.000001. Converting between prefixed and base units is a common exam skill.
Next useful steps
Need Help Applying This?
A 0625 specialist can work through the student's current paper or question and help identify whether the main difficulty is content, mathematics, practical reasoning or exam technique.