CIE A Level Biology (9700) 2019-2021

Revision Notes

1.1.2 Magnification Calculations

Magnification Calculations

  • Magnification is how many times bigger the image of a specimen observed is in comparison to the actual (real-life) size of the specimen
  • The magnification (M) of an object can be calculated if both the size of the image (I), and the actual size of the specimen (A), is known

Magnification Equation, IGCSE & GCSE Biology revision notes

An equation triangle for calculating magnification

Worked example: Magnification

An image of an animal cell is 30 mm in size and it has been magnified by a factor of X 3000.
What is the actual size of the cell?

To find the actual size of the cell:

Worked Example Using Magnification Equation, IGCSE & GCSE Biology revision notes

Worked example using the equation triangle for magnification


  • The size of cells is typically measured using the micrometre (μm) scale, with cellular structures measured in either micrometers (μm) or nanometers (nm)
  • When doing calculations all measurements must be in the same units. It is best to use the smallest unit of measurement shown in the question
  • To convert units, multiply or divide depending if the units are increasing or decreasing
  • Magnification does not have units

Converting Units, downloadable IGCSE & GCSE Biology revision notes

Converting units of measurement


  • There are 1000 nanometers (nm) in a micrometre (µm)
  • There are 1000 micrometres (µm) in a millimetre (mm)
  • There are 1000 millimetres (mm) in a metre (m)

Worked example: Magnification drawing

Example extended magnification question, IGCSE & GCSE Biology revision notes

Check that units in magnification questions are the same 

  • Remember that 1mm = 1000µm
  • 2000 / 1000 = 2, so the actual thickness of the leaf is 2 mm and the drawing thickness is 50 mm
  • Magnification = image size / actual size = 50 / 2 = 25
  • So the magnification is x 25

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