Student–Teacher Ratio Calculator
Work out a school’s pupil–teacher ratio from enrolment and full-time-equivalent teachers, the teachers needed for a target ratio, the students a staff can serve, staffing for a class size and timetable, the cost of extra teachers, and how the ratio compares with OECD, US and India norms.
How it works
Ratio = students ÷ FTE teachers · FTE = full-time teachers + part-timers × their average fraction · teachers needed = ⌈students ÷ target ratio⌉ · capacity = ⌊FTE × target ratio⌋ · timetable staffing = ⌈students × periods per student ÷ class size ÷ periods per teacher⌉
The pupil–teacher ratio divides enrolment by the number of teachers in full-time equivalents, so two half-time teachers count as one. Because it counts every teacher — including those planning, covering specialist subjects or teaching small groups — it is usually lower than the average class size. Switch “Solve for” to find how many teachers a target ratio needs (always rounded up, so the ratio stays at or under the target) or how many students a given staff can serve. For secondary schools the timetable matters more than the headline ratio: every student attends several periods a day, each class needs a teacher for each period, and each teacher teaches only some periods, so the calculator also works out the teachers needed to run every class at your class size. Add a cost per teacher to price the extra staff. As reference points, the OECD average is about 14 students per teacher in primary and 13 in secondary schools, US public schools averaged 15.4 in 2022–23, and India’s Right to Education Act sets 30:1 for primary and 35:1 for upper primary.
Worked example
640 students ÷ 22 teachers = 29.1 : 1, about 3.44 teachers per 100 students and 15.1 more students per teacher than the OECD primary average of about 14. For 25 : 1 you need ⌈640 ÷ 25⌉ = 26 teachers — four more; at $65,000 each that is $260,000 a year. The current 22 teachers could serve 22 × 25 = 550 students at the target. With classes of 32 and 8 periods a day, the school runs 640 × 8 ÷ 32 = 160 class periods daily, so teachers who teach 6 periods each are needed in ⌈160 ÷ 6⌉ = 27 posts.
Sources: NCES Common Core of Data — 2022–23 public school pupil/teacher ratio · OECD — Education at a Glance: student–teacher ratios and class size
Frequently asked questions
Are part-time teachers counted?
As fractions of full-time equivalent — two half-time teachers count as one. You can enter full-timers as FTE and add part-timers separately under More options with their average fraction.
Why is the class size bigger than the ratio?
Because teachers are not all in front of a class at once. Planning time, specialist roles and small-group teaching all add teachers without adding classes, so the class size is usually 1.2–1.6 times the ratio.
How many teachers do I need for a target ratio?
Divide the students by the target and round up: 500 students at 22 : 1 is 22.7, so 23 teachers. Rounding down would leave the ratio just above the target.
What is a good student–teacher ratio?
There is no single number. The OECD average is about 14 : 1 in primary and 13 : 1 in secondary education, and US public schools average about 15 : 1. Research links smaller ratios and classes to gains mainly in the early grades.
How do I staff a secondary timetable?
Multiply students by the periods each attends per day, divide by the class size to get class periods, then divide by the periods each teacher teaches. 640 students × 8 periods ÷ 32 per class ÷ 6 periods per teacher = 26.7, so 27 teachers.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.