1. Microscope Math
Biology 11

2. Don’t forget to always use units with numbers!
‘times larger’ or ‘x’
mm µm

3. Total Magnification Review
Formula:
Total Magnification =
(eyepiece)(objective)
Low: (10)(4) = 40x
Medium (10)(10) = 100x
High (10)(40) = 400x

4. Field of View
Diameter (widest distance across) of the circle of light when looking through the microscope
Expressed in µm (micrometers)

5. Micrometers (µm) 1 µm = 0.001 mm 1 mm = 1000 µm
To convert: Move decimal 3 places!
Example: 7752 µm
= 7.752mm

6. Measuring the Field Diameter (Low Power)
Place ruler across center of field of view
Line up the middle of a mm mark against one side of field of view
Count the number of full mm spaces.
Estimate amount of next
mm if not complete
Record results on board

7. Field Diameter Total Magnification Measurement (mm)
We will use the following field diameter sizes. Record the µm measurements on your sheet.
Total Magnification
Measurement (mm)
Field Diameter (µm)
Low (40x)
4.2
4200
Medium (100x)
1.68
1680
High (400x)
0.42
420

8. Estimating Specimen Size
If you know how wide your field of view is you can estimate the size of specimens being viewed
Expressed in µm (micrometers)

9. Estimating Specimen Size
Formula:
Estimated length = Field Diameter (µm)
Fit number

10. What is a “fit number”?
NUMBER of times an object FITS across the field of view
No units are used!

11. Example How many times can this ball fit across the field of view?
Fit number
is 3

12. If we viewed the ball with low power …
Formula:
Estimated length = Field of View (µm)
Fit number
= 4200 µm 3
= 1400 µm
Because it was viewed on low power

13. Any Questions?
Let’s practice!

14. Diagram Magnification
How many times larger your diagram (or scientific drawing) is than the actual specimen
Expressed as “times larger” or “X”

15. Diagram Magnification
Formula:
Diagram magnification =
Diagram size (µm)
Estimated Size

16. What is the “diagram size”?
How large your diagram (or scientific drawing)
Expressed in µm
How to find?
Measure your diagram in mm
Multiply by 1000

17. Example Diagram the “specimen” below. Determine the fit number.
Calculate the
estimated size.

18. Example (cont.) Determine the diagram size in micrometers.
Calculate the
diagram
magnification.

19. Any Questions?
Let’s practice!