Metal? Powder? Nanoparticles? 

What is expected size (millimeters, micrometers, nanometers)?

Is optical microscope of any help?

Hello Sir,

nano-particles. Fe2O3.

optical can't help.

You can make a suspension in alcohol and put a drop on TEM grid with a carbon film. Let it dry (it may be necessary to remove excess of water with a filter paper, carefully applying it to the edge of a grid). Use some image analysis software (such as ImageJ) for measurements.

You can use the help of "Image J" software. You tube links will give the use of Image J software. You can actually calculate upto the inter atomic distances using the TEM images.

Firstly, the sample powder was ultrasonically dispersed in alcohol and then deposited on a holey carbon-coated copper grid. Secondly, based on the obtained TEM images, you can utilize Nano Measurer software to analyze the nano-partical size.

Hello dear friends,

image j software will give us particle size. in the case of nano particles, the crystallite size and particle size might be the same. but if the particle is bigger than the crystallite size. is there any direct method to calculate crystallite size as we calculate from FWHM in XRD.?

I see what you're asking. Shoortly: no. Magnify the particles untill you see interatomic distances (fringes): then you can determine the size of crystallites and if they're the same as particles, or there are many crystallites agglomerated into a particle. 

Thanks, Janez Zavašnik. let me try it first. will come back if stuck somewhere :)

no but i guess it is easily available in papers. Using these kind of images as given above are available in papers