What is microscope magnification?
Enter the eyepiece and objective powers to get the total magnification of a compound microscope, and the eyepiece field number to get the field of view. The calculator also scales a field of view to another magnification, finds a specimen’s actual size from its image, and the magnification of an image.
- Answer
- 400×; field of view 0.5 mm (500 µm)
400×; field of view 0.5 mm (500 µm).
- Magnification (×)
- 400
- Field of view (mm)
- 0.5
- Field of view (µm)
- 500
Answer: 400×; field of view 0.5 mm (500 µm). 400×; field of view 0.5 mm (500 µm).
How to calculate
Finds a compound microscope’s total magnification from the eyepiece and objective, the field of view from the field number, the field of view at another magnification, a specimen’s actual size from its image, or the magnification of an image.
Example with the default inputs (Find Total magnification, Eyepiece (ocular) power (×) 10, Objective power (×) 40, Eyepiece field number (mm) 20): 400×; field of view 0.5 mm (500 µm).
Method: Total magnification = eyepiece × objective; field of view = field number ÷ objective; FOV₂ = FOV₁ × M₁ ÷ M₂; actual size = image size ÷ magnification; magnification = image size ÷ actual size.
- A compound light microscope with no extra magnification between the objective and the eyepiece (no zoom or magnification changer).
- The field of view scales with the objective when the eyepiece stays the same, so total magnifications compare the same way.
Worked examples
Each example is checked against the calculator on every build.
- Find Total magnification, Eyepiece (ocular) power (×) 10, Objective power (×) 40, Eyepiece field number (mm) 20 gives Magnification (×) 400, Field of view (mm) 0.5, Field of view (µm) 500, Answer 400×; field of view 0.5 mm (500 µm).Source: OpenStax, Microbiology, §2.3 Instruments of Microscopy (total magnification = ocular × objective; 10× ocular with a 40× objective is 400×), https://openstax.org/books/microbiology/pages/2-3-instruments-of-microscopy; Nikon, Glossary of Microscopy Terms: field of view (field number ÷ objective magnification, in mm), https://www.microscope.healthcare.nikon.com/resources/glossary/field-of-view: 20 ÷ 40 = 0.5 mm
- Find Total magnification, Eyepiece (ocular) power (×) 10, Objective power (×) 100 gives Magnification (×) 1,000, Answer 1,000×.Source: OpenStax, Microbiology, §2.3 Instruments of Microscopy (total magnification = ocular × objective; 10× ocular with a 40× objective is 400×), https://openstax.org/books/microbiology/pages/2-3-instruments-of-microscopy: objectives from 4× to 100×, oculars usually 10×
- Find Field of view, Field of view you know 4.5 mm, Its total magnification (×) 40, New total magnification (×) 400 gives Field of view (mm) 0.45, Field of view (µm) 450.Source: Nikon, Glossary of Microscopy Terms: field of view (field number ÷ objective magnification, in mm), https://www.microscope.healthcare.nikon.com/resources/glossary/field-of-view: the field of view is the field number ÷ the objective, so it scales as 1 ÷ magnification
- Find Actual size, Image size 50 mm, Magnification (×) 2,000 gives Actual size (µm) 25, Actual size (mm) 0.025, Answer Actual size 25 µm (0.025 mm).Source: OpenStax, University Physics Volume 3, §2.4 Thin Lenses (m = h_i ÷ h_o, equation 2.22), https://openstax.org/books/university-physics-volume-3/pages/2-4-thin-lenses: object size = image size ÷ m
- Find Image magnification, Image size 50 mm, Actual size 25 µm gives Magnification (×) 2,000, Answer Magnification 2,000×.Source: OpenStax, University Physics Volume 3, §2.4 Thin Lenses (m = h_i ÷ h_o, equation 2.22), https://openstax.org/books/university-physics-volume-3/pages/2-4-thin-lenses
How it works
Total magnification (OpenStax Microbiology §2.3).
Total magnification = eyepiece power × objective power
Field of view (Nikon). The diameter of the circle you see at the specimen:
Field of view (mm) = field number (mm) ÷ objective power
The field number is the eyepiece’s field stop diameter. Leave it empty to skip the field of view. The page shows the field of view in mm and µm (1 mm = 1,000 µm).
Field of view at another magnification. With the same eyepiece the field of view is the field number ÷ the objective, so it goes as 1 ÷ magnification:
FOV₂ = FOV₁ × M₁ ÷ M₂
with M₁ and M₂ the total magnifications. Type FOV₁ in mm, cm, µm or nm.
Actual size and magnification of an image (OpenStax University Physics 3, m = h_i ÷ h_o).
- Actual size = image size ÷ magnification
- Magnification = image size ÷ actual size
Sizes in mm, cm, µm or nm, read back exactly as typed (1 cm = 10,000 µm, 1 mm = 1,000 µm, 1 nm = 0.001 µm). The actual size is shown in µm and mm.
Rules the page checks. Eyepiece from 1× to 100×; objective from 0.1× to 1,000×; field number from 0.1 to 100 mm; the known field of view, the image size and the actual size each from 10⁻¹⁵ m (0.000001 nm) to 1,000 m; total magnifications from 0.1× to 10⁹×; the image’s magnification from 10⁻⁶ to 10⁹.
How results are written. Every result is worked exactly from the typed decimals and rounded once: 6 significant figures, trailing zeros dropped, thousands commas, and m × 10ⁿ below 0.000001 or from 10²¹. The sentence reads “400×; field of view 0.5 mm (500 µm)” (just “400×” with no field number), “Field of view 0.45 mm (450 µm)”, “Actual size 25 µm (0.025 mm)” or “Magnification 2,000×”.
Assumptions. A compound light microscope with nothing magnifying between the objective and the eyepiece, such as a zoom or magnification changer.
Worked examples by hand
10× eyepiece, 40× objective, field number 20. 10 × 40 = 400×; field of view 20 ÷ 40 = 0.5 mm (500 µm).
10× eyepiece, 100× oil-immersion objective. 10 × 100 = 1,000×.
Field of view at 400×. 4.5 mm at 40×: 4.5 × 40 ÷ 400 = 0.45 mm (450 µm).
Actual size. An image 50 mm across at 2,000×: 50,000 µm ÷ 2,000 = 25 µm (0.025 mm).
Magnification of an image. A 25 µm cell drawn 50 mm across: 50,000 µm ÷ 25 µm = 2,000×.
Other questions people ask
How do you find the total magnification of a microscope?
Multiply the eyepiece (ocular) power by the objective power. A 10× eyepiece with a 40× objective magnifies 10 × 40 = 400 times; with the 100× oil-immersion objective it is 1,000×.
How do I work out the field of view?
Divide the eyepiece’s field number by the objective power. The field number, in millimeters, is printed on the eyepiece: a field number of 20 with a 40× objective gives a field of view 20 ÷ 40 = 0.5 mm (500 µm) across.
How does the field of view change at higher magnification?
It shrinks in the same proportion. A field 4.5 mm across at 40× is 4.5 × 40 ÷ 400 = 0.45 mm across at 400×, with the same eyepiece.
How do I calculate the actual size of a specimen?
Divide the image size by the magnification, in the same units. A cell 50 mm across in a drawing at 2,000× is 50 ÷ 2,000 = 0.025 mm, or 25 µm, across.
How do I calculate magnification from a drawing or photo?
Divide the image size by the actual size, after putting both in the same unit. An image 50 mm long of a 25 µm cell: 50 mm = 50,000 µm, and 50,000 ÷ 25 = 2,000×.
Does a higher magnification always show more detail?
No. Detail depends on resolution, which a light microscope reaches at about 1,000×. Beyond that the image gets bigger but not sharper (OpenStax Microbiology).