Adding scale bars to images using ImageJ


1) Install ImageJ on your computer if it is not installed already.  You can download ImageJ from


2) Start ImageJ:



3) If you have an image with a calibration scale (ie a ruler or a stage micrometer) open the image.  (If you don’t go to step 4 and you can enter the scale information directly into the ‘Set Scale’ dialog.)  Select the straight line selection tool:



Now draw a straight line that defines a known distance on your calibration image (5mm in this case):



4) In the ‘Analyze’ menu select ‘Set Scale’.  The following dialog box will open:



The distance in pixels will be filled in for you based on the length of the line you drew in step 3.  If you know your calibration values just enter the number of pixels in a known distance.  Fill in the ‘Known distance’ (in this case 5mm) without units.  Define the units of length in the ‘Unit of Length’ field.  Click on ‘Global’ so that this calibration applies to all images that you open in this ImageJ session.  Click ‘OK’.


5) Now open the image you want to add a scale bar to.  In the ‘Analyze/Tools’ menu select ‘Scale Bar’.  The scale bar dialog will open and a scale bar will appear on your image.  You can adjust the size, color, and placement of your scale bar.  Once you are finished click on ‘OK”, save your image, and you are done.