Square mm of defined area, help very much appreciated

Dear ImageJ Community,
If possible i kindly ask for help. I would like to measure with imageJ the shown are in Square mm as i have a lenght scale in mm as seen in the picture attached. If you could please tell me how to do this.

Thank you in advance,

Hi @Nadal,

Welcome to the forum (and congrats for your last grand Slam :slight_smile: )

The best thing to do is to calibrate your images (Images>Properties). Doing this, all you measurements (including area) will be calibrated and her, you result will be expressed as mm².

All this is explained here : Spatial Calibration of an image


Ps : of course, all this can be automated in a script if you have lots of images

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Ciao Nico!

Thank you for your kind reply!

I just calibrated the Image with these steps:

  1. Line Tool: 1mm = lenght = 29pixel

2.Set Scale

Distance in pixel 29

Known Distance 1

Unit of lenght mm

Now if i mark an area usino the Freehand Tool and Measure, do i get squaremm in the Area Field? And could you maybe tell me what in this case mean/min an Max stands for, because i doubt that this area is really 33square mm in reality…so i think i have
an error somewhere.

If you have an idea i would gladly hear it! Greetings from Austria,


Hi @Nadal,

Mean, Max and Min are measurements made on pixel greylevels inside ROI.
I’ve tested your print screen image. I find an area in the same range (~40 mm²), so I fell you’re right. Why do you feel this ROI couldn’t be 33mm² ?


Ciao Nico,

Sorry for the late reply.

Thank you for the doublecheck - i will make some more tests and if in doubt i may write you again :wink:

Thank you a lot for your help!

best wishes froh austria