If you don't know (minimally) the fully diluted count of shares in the company, your option grant is as specific is saying that your salary will be denominated in dollars and you'll be given more detail about it sometime after joining the company, pinky-swear.
A company which won't provide enough information to value an option grant contemporaneous with the written offer is being either abusive or stupid. There exist employment opportunities at companies which are neither abusive nor stupid. Take one of those instead.
Sounds like I was right to pass on the company that promised me "4000 options" and insisted that any details beyond that were strictly confidential and could under no circumstances be disclosed to any non-employees. It seemed especially suspicious in conjunction with the rest of their attempts at hard-sell tactics that just left a bad taste in my mouth.
Thanks! My first two startup jobs, were purely based on the number of options. Fortunately, my current one gave me enough insight about it before, and much more in depth after. There's so much to know about how options work, most people dont realize when moving to a startup job for the first time!
A company which won't provide enough information to value an option grant contemporaneous with the written offer is being either abusive or stupid. There exist employment opportunities at companies which are neither abusive nor stupid. Take one of those instead.