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SI units and prefixes flash cards

Flash cards on the seven SI base units, common derived units such as the newton, joule and watt, and the prefixes from pico to tera with their powers of ten.

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The cards, front and back

  1. 1
    Front

    What is the SI system?

    Back

    The International System of Units, the standard set of units used in science around the world. It has seven base units, and all other units are made from them.

  2. 2
    Front

    SI base unit of length

    Back

    The metre (m).

  3. 3
    Front

    SI base unit of mass

    Back

    The kilogram (kg). It is the only base unit with a prefix in its name.

  4. 4
    Front

    SI base unit of time

    Back

    The second (s).

  5. 5
    Front

    SI base unit of electric current

    Back

    The ampere (A), often shortened to amp.

  6. 6
    Front

    SI base unit of temperature

    Back

    The kelvin (K). To convert, kelvin = degrees Celsius + 273.15 (often rounded to 273). Note there is no degree sign with kelvin.

  7. 7
    Front

    SI base unit of amount of substance

    Back

    The mole (mol).

  8. 8
    Front

    SI base unit of luminous intensity

    Back

    The candela (cd).

  9. 9
    Front

    The newton (N)

    Back

    The unit of force. 1 N is the force that gives a 1 kg mass an acceleration of 1 m/s², so 1 N = 1 kg m/s².

  10. 10
    Front

    The joule (J)

    Back

    The unit of energy and work. 1 J is the work done when a force of 1 N moves an object 1 m, so 1 J = 1 N m.

  11. 11
    Front

    The watt (W)

    Back

    The unit of power. 1 W = 1 joule per second.

  12. 12
    Front

    The pascal (Pa)

    Back

    The unit of pressure. 1 Pa = 1 newton per square metre (N/m²).

  13. 13
    Front

    The coulomb (C), volt (V) and ohm (Ω)

    Back

    The coulomb is the unit of charge (1 C = 1 A s). The volt is the unit of potential difference (1 V = 1 J/C). The ohm is the unit of resistance (1 Ω = 1 V/A).

  14. 14
    Front

    The hertz (Hz)

    Back

    The unit of frequency. 1 Hz is one cycle per second.

  15. 15
    Front

    Prefixes tera (T) and giga (G)

    Back

    Tera means × 10^12 (a million million). Giga means × 10^9 (a thousand million).

  16. 16
    Front

    Prefixes mega (M) and kilo (k)

    Back

    Mega means × 10^6 (a million). Kilo means × 10^3 (a thousand).

  17. 17
    Front

    Prefixes centi (c) and milli (m)

    Back

    Centi means × 10^−2 (a hundredth). Milli means × 10^−3 (a thousandth).

  18. 18
    Front

    Prefixes micro (μ) and nano (n)

    Back

    Micro means × 10^−6 (a millionth). Nano means × 10^−9 (a thousand-millionth).

  19. 19
    Front

    Prefix pico (p)

    Back

    Pico means × 10^−12 (a million-millionth).

  20. 20
    Front

    Why does the case of a symbol matter?

    Back

    Capital M means mega (a million) but small m means milli (a thousandth) or metre. A small k is kilo, and capital K is kelvin.

  21. 21
    Front

    Convert 2.5 km to metres, and 450 mA to amperes.

    Back

    2.5 km = 2.5 × 1000 = 2500 m. 450 mA = 450 ÷ 1000 = 0.45 A.

  22. 22
    Front

    How many square centimetres are in a square metre, and cubic centimetres in a cubic metre?

    Back

    1 m² = 100 × 100 = 10 000 cm². 1 m³ = 100 × 100 × 100 = 1 000 000 cm³. Square and cube the conversion factor, not just multiply by 100.

  23. 23
    Front

    How do litres relate to SI units?

    Back

    The litre is not an SI unit but is accepted for use with it. 1 litre = 1000 cm³ = 1 dm³, and 1000 litres = 1 m³.

How to use this template

This deck teaches the units every science course relies on. It covers the seven SI base units, the main derived units (newton, joule, watt, pascal, coulomb, volt, ohm and hertz) and what each is made from, the prefixes from pico to tera with their powers of ten, why capital and small letters matter, converting between prefixes, area and volume units, and how the litre fits in. It suits Year 7 to Year 11 science, GCSE and IGCSE physics and chemistry, high school science, and first-year university students who want a quick reset before lab work. Learn it with Learn mode, then Test mode, and let spaced repetition keep the prefixes fresh. Print it double-sided to keep next to your calculator.

Tips

  • Learn the prefixes as a ladder in steps of a thousand, from pico to tera, with centi as the odd one out.
  • Always write the unit after every number in your working, so you can see if the units make sense.
  • To check a derived unit, break it into base units. If the base units on both sides of an equation match, the equation is likely set up correctly.
  • When converting areas and volumes, square or cube the conversion factor. This is the most common unit mistake.
  • Practise writing numbers in standard form with these prefixes, such as 3 μm = 3 × 10^−6 m.

Make it fit

  • Add the units your course uses most, such as mol/dm³ in chemistry or kWh in physics.
  • Add cards for imperial or US customary units if you need to convert from them.
  • Make reverse cards with the power of ten on the front and the prefix on the back.
  • Split the deck into base units, derived units and prefixes.

Updated October 28, 2026

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