Your RRSP contribution for any given year is the lower of:
- 18% of your earned income from the previous year
- The maximum annual contribution limit for the taxation year (posted by the CRA online)
- The remaining limit after any company sponsored pension plan contribution
Any unused contribution room from 1991 onwards can be carried forward to the current year. Every Canadian is allowed to over-contribute $2,000 once in their lifetime but if you over-contribute beyond this amount, you'll be charged a penalty tax of 1% of the over-contribution amount per month.
You can read more about RRSP contributions and see the maximum contribution limit for each year on the Canadian Revenue Agency website.