Biology · Introductory biology · Worked example
Find a cell’s actual size from a scale bar
On a printed micrograph, a 10 µm scale bar measures 25 mm, and a cell measures 60 mm across. Find the magnification and the cell’s actual diameter.
Convert the bar’s image length
Put both lengths in micrometres: 25 mm is 25,000 µm.
Find the magnification
Divide the bar’s image length by the real length it represents.
Find the actual size
The cell measures 60 mm, or 60,000 µm, on the image. Divide by the magnification.
Check with a proportion
On the image the cell is 60/25 = 2.4 times as long as the bar, so in reality it is 2.4 times the bar’s 10 µm.
Result
The magnification is 2,500×, and the cell is 24 µm across.
Your turn
On a screen, a 5 µm scale bar measures 15 mm and a mitochondrion measures 6 mm long. Find the magnification and the mitochondrion’s length.
Show the answer and explanation
3,000×, and 2 µm long.
15 mm = 15,000 µm, so the magnification is 15,000/5 = 3,000. The mitochondrion is 6,000 µm/3,000 = 2 µm long, which is also 6/15 of the 5 µm bar.
Keep exploring
The scale-bar tool opens in magnification mode for a print 150 mm wide at 2,500×. It confirms that a 10 µm bar is 25 mm long on the print, or 250 of 1,500 pixels.
Return to the concept →Sources and scope
Authored study material. Tool results depend on the stated inputs and model assumptions.
Try in the workspace
Open the example inputs, change a value and keep a useful result on your board.
Open the scale-bar tool Open worked example on a board Microscopy referenceYour existing work stays on this device. Examples open as editable copies.