i would like to ask what is the current percentage that photoshop uses for default grayscale conversion? It used to be 59 green 30 red and 11 blue but seems to be no longer the case.
Thank you very much
Conversion to what and from what? This depends entirely on the specific icc profiles (RGB and gray).
There's an additional catch, which is probably what you're referring to: A grayscale conversion from RGB isn't a simple average desaturation. It goes via Lab as the Profile Connection Space, and that means the inherent luminance of any color factors in. This way a bright yellow remains light, and a dark purple remains dark. If it was just R=G=B, they'd both end up mid-gray.
It's easier to illustrate than to explain:
IOW, to answer the question, there's no percentage formula, never was. It's just Lab, converted further to a grayscale profile.
You might get such a formula to work as an approximation, but it would only be valid in special circumstances. It wouldn't, and couldn't, be universal. And there's no point. Just go via Lab and you'll get there.