How OMSAS converts your grades: a worked example
Every Ontario medical school sees the same GPA from OMSAS before applying its own rules. That number is built from three ingredients: a conversion table that maps your transcript grades onto a 4.0 scale, a weight for each course, and one division at the end. This article walks through all three on a small, realistic transcript.
Step 1: which scale is yours
The OUAC conversion page lists nine scales and tells you which one each Canadian university uses. Scales 3 to 6 are percentage bands, scales 7 to 9 are letter grades, and scales 1 and 2 are the older 9-point and 8-point numeric systems. Western, Guelph, Queen's and most Ontario schools that print percentages are on scale 3; McMaster, Ottawa and most schools that print letters are on scale 7; McGill is on scale 8 and York and Manitoba on scale 9. A few universities appear under two scales (Toronto, Queen's, Waterloo, Windsor, Victoria) because different faculties print grades differently; OMSAS uses whichever matches the format on your transcript.
The scales are not interchangeable. On scale 3, 85 to 89 becomes 3.90 and 90 or above becomes 4.00. On scale 4, you need 93 for a 4.00. On scale 7, an A is 3.90 and only an A+ is 4.00, while on scale 8 an A is already 4.00. This is why two students with "the same" grades from different universities can have different OMSAS GPAs, and it is not something you can fix. It is also why a generic calculator that applies one scale to everyone is unreliable.
Step 2: weights
OMSAS gives each course a weight by length: a full-year course counts 2, a one-term (half-year) course counts 1, a three-quarter course counts 1.5 and a lab course counts 0.5. The weight has nothing to do with difficulty or year level. Two half-courses weigh the same as one full-year course.
Step 3: the arithmetic
For every course, multiply the converted grade by its weight. Add all of those products together. Divide by the total weight. That is the cumulative GPA. OUAC states plainly that it is not an average of averages, so a strong year does not "count once" against a weak year; each course counts by its own weight wherever it sits.
A worked example
Take a student on scale 3 with this record. Converted values come straight from the table.
| Course | Grade | Weight | Converted | Grade × weight |
|---|---|---|---|---|
| Biology, full year | 86 | 2.0 | 3.90 | 7.80 |
| Chemistry, full year | 82 | 2.0 | 3.70 | 7.40 |
| Calculus, fall | 78 | 1.0 | 3.30 | 3.30 |
| Calculus, winter | 74 | 1.0 | 3.00 | 3.00 |
| Psychology, fall | 88 | 1.0 | 3.90 | 3.90 |
| Physics, winter | 79 | 1.0 | 3.30 | 3.30 |
| Writing, full year | 84 | 2.0 | 3.70 | 7.40 |
| Chemistry lab | 91 | 0.5 | 4.00 | 2.00 |
| Total | 10.5 | 38.10 |
38.10 divided by 10.5 is 3.63. Notice what happened to the 79 in physics: it fell one point short of the 80 to 84 band and cost 0.40 on that course. Notice also that the simple percentage average of these grades is about 82.8, which would be 3.70 if it were converted as a single number. OMSAS does not do that. It converts each course first, and the bands are not linear, so the result lands at 3.63.
What is left out
OMSAS includes every undergraduate credit course from a Canadian or American university, including repeated courses (both attempts), failures and supplementals, and courses that were extra to your degree. It excludes college and CEGEP courses, graduate courses, MD-program courses, continuing education, challenge-for-credit, AP and IB, consecutive B.Ed. courses, and pass/credit grades, although a fail still counts as zero. The full list is on the OMSAS GPA calculations page.
The practical lesson
Because the bands are steps, the marks that matter most are the ones sitting one or two points below a boundary. A 79 that becomes an 80 is worth 0.40 on that course; a 92 that becomes a 95 is worth nothing on scale 3. If you are choosing where to put your last week of studying, put it in the course that is closest to a boundary from below. And because full-year courses weigh double, a bad grade in a full-year course does twice the damage of the same grade in a one-term elective.
This article describes published rules as understood on 2026-09-06. Rules change each cycle; the linked official pages are the authority. Not affiliated with OUAC, the AAMC or any school.