Once you have decided on the percentage of shares to reserve for your ESOP, you will need to determine the actual number of shares that the percentage represents. You can use the Clara calculator, which can be accessed at https://calculator.clara.co/percentages, to calculate this number.
It's important to note that when implementing vesting schedules, you may need to allocate a slightly higher number of shares. For example, suppose you have 90 issued shares and have reserved 10 shares for the ESOP, and you have promised someone 2 shares. In that case, this would not be enough to create a workable vesting schedule because over a 48-month vesting period, those 2 shares would only result in 0.04 shares vested per month. Since fractional shares cannot be issued, you will need to adjust your share allocation to ensure that it allows for a feasible vesting schedule.