You may want to use stereo measurements (from stereo pairs, not from photometric reconstruction, which is unreliable). It requires a lot of time and additional software.

https://en.wikipedia.org/wiki/Scanning_electron_microscope#3D_in_SEM

If you are lucky and your objects are rigid and mostly orthogonal to a surface you can try to mount your specimen so that its surface will be parallel to a beam (orthogonal to a specimen stage) and measure length of objects directly.

You may want to use stereo measurements (from stereo pairs, not from photometric reconstruction, which is unreliable). It requires a lot of time and additional software.

https://en.wikipedia.org/wiki/Scanning_electron_microscope#3D_in_SEM

If you are lucky and your objects are rigid and mostly orthogonal to a surface you can try to mount your specimen so that its surface will be parallel to a beam (orthogonal to a specimen stage) and measure length of objects directly.

Dear Rizwan ,

As valdimir said you have two options to measure your object's length, you can use FeSEM in that you have this option to measure the length of the object directly. and another option is you have to use some other software to measure this. some online software are available or u can download them and use.

SI viewer and imageJ (NIH) both software can help you.

in image J, you first need to calibrate the scale bar (along with measurement unit) and then, can measure the length of target accordingly.

@ Manish Yadav @ Meenakshi Maurya

thanks a lot

You do not need any FeSEM. You either need a stereo pair image like Vladimir said, or You need to tilt Your specimen, so Your hair would be perpendicular to the beam. If You have a 4 or 5 segment backscatter detector (BSD), You can sequentially take pictures of the same spot with only one BSD segment switched on (or positively biased) at a time. Then, You can use some software to make a 3D image and measure what You want.