How much can my employer who set up a SEP contribute?

SEP IRAs permit employers to make a maximum contribution of up to the lesser of (i) 25% of compensation or (ii) $53,000 (for 2016) or $54,000 (for 2017) and subject to annual cost-of-living adjustments for later years. 

SEP IRA rules also state that an employer must make contributions proportional to its employees' salaries, meaning that each eligible employee’s contribution must be the same percentage of salary for the calendar year.

IRS Website - SEP plan FAQ