AQA A Level Biology

Revision Notes

2.2.5 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

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

  • 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

Example-extended-magnification-question, downloadable AS & A Level Biology revision notes

Step 1: 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

Step 2: Calculate Magnification

Magnification = image size / actual size = 50 / 2 = 25

So the magnification is x 25


Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.

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