CALCULATING MAGNIFICATION
Magnification is the increase in the apparent size of an object.
http://www.ibguides.com/biology/notes/membranes
http://www.youtube.com/watch?v=wPYBLysk12M
calculating magnification you tube
The notation “LM 1,000x” printed along the right edge of the micrograph tells us
that the photograph was taken through a light microscope and that the image is
about 1,000 times the actual size of the organism.
Refer to page number 52 and 53 in your text book.
At higher magnification, the image would begin to blur. Light microscopes can
effectively magnify objects only about 1,000 times.
Calculate the linear magnification of drawings and the
actual size of specimens in images of known magnification.





Take a measurement of the drawing (width or length)
Take this same measurement of the specimen
Remember to convert units if needed to
Place your values into the equation
Magnification = length of drawing / length of actual specimen
You can also calculate the length of the specimen if this is unknown: length of the drawing /
magnification.
Conversion of units:
1 centimeter = 10-2 meters
1 millimeter = 10-3 meters
1 micrometer = 10-6 meters
1 nanometer = 10-9 meters
The general formula for calculation of magnification is
Magnification = drawing size/actual size
Actual size = Drawing size/ magnification
Measurement equivalents
1 centimeter (cm) = 10-2m (1/100m)
I millimeter (mm) = 10-3m (1/1,000m)
I micrometer (µm) = 10-6m (1/1,000,000m)
1 nanometer (nm) = 10-9m (1/1,000,000,000m)
1000 mm = 1 m
1000 µm = 1 mm
1000 nm = µm
Converting to actual size when magnification is given
 If the micrograph has a magnification of 1000x, then everything is shown 1000 times
larger than it actually is. If you measure an object to be 15 mm, it is actually 1000x
smaller. 15 mm divided by 1000 = 0.015 mm or 15 m. Thus, 15 m is the actual size of
the object you measured to be 15 mm on the micrograph.
If the magnification is given, then we need to measure the size of the object and
divide it by magnification to get the actual size of the specimen. Make sure the
units are the same.
 To convert to actual size, divide by the magnification. Watch those units! The
magnification itself has NO UNITS because it is a ratio.
(size in mm measured on micrograph) = actual size in mm
(magnification)
 You may want to include a conversion factor in your equation to convert the units
right away. When converting from mm to m do you divide or multiply by 1000?

Converting to actual size using a scale bar
 Your own textbook has micrographs of cells & cell structures and gives a scale bar
instead of magnification for all of its figures. This is useful in publishing because any
size change during printing will automatically change both the micrograph and the scale
bar equally. Therefore, you will often encounter the use of scale bars for micrographs.
 The actual size that corresponds to the drawn scale bar is given. Use this to make a
conversion factor to convert measured distances to actual size:
(size in mm measured on micrograph)
x
(actual size of scale bar)
= actual size
(measured size of scale bar in mm)
 If you measured the organelle or bacterium in mm and the scale bar in mm, these
units will cancel and your answer will now have the units shown for the actual size of the
scale bar.
The general formula for calculation magnification is:
Magnification =
drawing size
Actual size
M= D
A
You must ALWAYS use the same units for drawing size and actual size for this equation to work!
Complete the following
Actual Specimen Size Drawing Size
0.5 mm
2 cm
200 m
1 cm
40 m
2 cm
100 m
Drawing
Magnification
200X
5 cm
100X
4 cm
50X
2. If a microorganisms is 2cm long and the magnification is 1000x, how long will
the drawing be?
3. A student draws a cell diagram 24mm long. She writes 400X below the
diagram. How large is the actual cell?
4. A cell is 80 m in length. If drawn 600 times actual size, how long will the
drawing be in cm?
5. Complete the chart
Drawing Size
Actual Size
10mm
100m
4mm
10cm
Drawing
Magnification
3X
25X
150mm
15m
0.8cm
8m