hair density

I have 2 planes (grass courts), one is small and one is big.
There is a hair particle system on the small one (for example emission number 100).

If I apply the same particle system to the big one, emission number is still 100, but the density will be lower because I apply particle system on bigger area.
My question is, is it possible to automatic change emission number according to the area size? (to have the same density on both planes)

automatically? I don’t think so, but you can set up 2 particle systems and make each plane its own object. I assume both your planes are not separate meshes.

In my case, I have several planes (all are separate objects), setting up particle system for every one to have the same look is a bit difficult.

Not really if you do it correctly. Faces set to random. You should be able to set it up so that just increasing the number will make the larger or smaller planes look nearly identical. I just woke up. Give me a while to drink my coffee and I’ll test this theory in blender and repost some more solid solutions. I don’t make hair on a regular basis.

Yes of course, you are right that I can just increase the number of particles. I was just curious, if it is possible to set for example 100 hair for 1square cm. I have several grass courts, so it is a bit time consuming because there is a lot of hairs (+children) so I don’t see the right density in 3D view. I have to render the image for every one setting

I’m not sure that is possible out the box, but it sounds like a very simple script could do that. Might try posting a request in the python area of this forum for someone to make it for you.