Short answer. For each subject, Z = (your mark - mean) / SD. The A/L Z-score is the average of the Z-scores of your three subjects. You need the subject mean and SD from official results.
How the Z-score works
Sri Lanka uses the Z-score to rank A/L students for university places. The score compares your mark with the marks of all students in the same subject. So a hard subject and an easy subject can be placed on one scale.
For one subject, the formula is:
Z = (your mark - mean) / SD
The mean is the average mark in that subject. The SD, or standard deviation, shows how spread out the marks are. A Z of 0 means you scored at the mean. A Z of 1 means you scored one SD above it.
The Z-score for admission is the average of the Z-scores of your three subjects. Add the three values and divide by 3.
What this page can and cannot do. I could not confirm a public source that lists the subject mean and SD for every subject and year. Two sources say the figures exist, but they name different bodies, and I could not open a primary table. So this page does not guess them. You type the mean and SD yourself, from the official results sheet or notice you hold. Then the page does the sums.
The result is a formula result. It is not a rank, and it is not a district cut-off. Selection also uses district quotas, course cut-offs and other rules. Also, a pass in all three subjects is needed.
Some experts argue that pooling marks across groups can distort the score. That is a debate about the method, and it does not change the arithmetic here.
How to use the result
Type your mark in each subject. Then type the mean and the SD for the same subject and year. Both must come from the same group of students as your mark. The tool shows each subject Z-score and the average. Compare subjects to see where you did best against your group.
Use the result to understand the method, not to forecast a place. Compare your real Z-score with the published cut-off for your course and district when the official list comes out.
Sources
Grading rules checked 2026-10-10 against these pages. Rules change, so confirm with your school, board or university before you rely on a number.
Worked example
Example. These numbers are made up to show the sums. They are not real results.
Physics: mark 78, mean 48, SD 16. Z = 30 / 16 = 1.875. Chemistry: mark 70, mean 45, SD 20. Z = 1.25. Combined Maths: mark 66, mean 40, SD 22. Z = 1.18.
Average: (1.875 + 1.25 + 1.18) / 3 = 1.44.
Questions
Where do I find the mean and SD?
I could not confirm a public table for every subject and year. Use the official results sheet or notice you have. This page does not guess them.
What is a good Z-score?
It depends on your course and district cut-offs for the year. A Z above 0 means you scored above the mean of your subjects.
Does the tool predict if I get a place?
No. Selection uses district quotas, course cut-offs and other rules. This page only does the Z-score sums.
Can the Z-score be negative?
Yes. If your marks are below the mean in your subjects, the Z-score is below zero.
What if I sat four subjects?
Sources say the best three are used. Enter your three best subjects.
Last checked by the StudyCount team.