Sahel EDU

Marking out of 10, 20, 100 or in letters: converting without distorting the average

Converting a mark from one scale to another is a rule of three: multiply the mark by the new maximum and divide by the old one. Mistakes come from not converting before averaging, or from the way several assessments are combined. This guide gives the rule, exact examples, what to do with averages and thresholds, and what does not convert exactly: letters and points.

The rule of three: bringing a mark to out of 20

To go from a mark out of A to a mark out of B: new mark = old mark × B ÷ A. To bring a mark out of 10 to out of 20, multiply by 2; out of 5, multiply by 4; out of 100, divide by 5. Keep the decimals and round only the final result.

A mark out of 20 remains the rule in French-speaking secondary schools in Cameroon. In primary school, the official text sets neither the maximum mark nor the labels of the competency levels: the school chooses its scale, which it converts if it wants to compare it or combine it with another.

7 out of 10 gives 7 × 20 ÷ 10 = 14 out of 20.
3.5 out of 5 gives 3.5 × 20 ÷ 5 = 14 out of 20.
63 out of 100 gives 63 × 20 ÷ 100 = 12.6 out of 20.
17 out of 25 gives 17 × 20 ÷ 25 = 13.6 out of 20.
45 out of 60 gives 45 × 20 ÷ 60 = 15 out of 20.
The other way round, 13 out of 20 is worth 6.5 out of 10 and 65 out of 100.

Why convert before averaging

A student gets 8 out of 10 in a quiz and 12 out of 20 in a test in the same subject. The “by eye” average of the two numbers gives (8 + 12) ÷ 2 = 10: it suggests a student who barely passes. But 8 out of 10 is worth 16 out of 20, and the right average is (16 + 12) ÷ 2 = 14. The four-mark error comes from mixing scales.

The rule is therefore simple: every mark is first brought to the scale of the average, and only then is the calculation made. This conversion applies to the assessments in a subject, and to the subject averages before the general average is worked out.

Several assessments: equal, or weighted by their scale?

Two ways of combining assessments with different scales give different results. Take a quiz of 8 out of 10 and a test of 12 out of 40. Each assessment counts equally, once brought to out of 20: 16 and 6, giving an average of 11. Or the points are added up: (8 + 12) ÷ (10 + 40) = 0.4, or 8 out of 20.

No national text that we found settles the matter. Common practice is the first: each assessment weighs the same, unless a weighting is written in the school rules, because a longer paper is not necessarily more important. The essential thing is to choose once, write it down, and apply it to every class.

Equal assessments after conversion: 11 out of 20 in the example.
Points added up: 8 out of 20 in the example, with the long test weighing more.

Converting averages, thresholds and grades

The same proportions apply to averages, pass marks and grades: everything is read as a percentage of the maximum.

The pass mark of 10 out of 20 is 5 out of 10, 2.5 out of 5 and 50 out of 100.
A distinction threshold set out of 20 is converted to the school’s scale: 12 out of 20 becomes 6 out of 10 or 60 out of 100.
Grades (pass, fairly good, good…) are defined as percentages or out of 20; move them to another scale together with their band, never separately.
Never round a converted mark before averaging it: the roundings add up.
Do not convert twice: always start again from the original mark.

Letters, points and GPA: what does not convert exactly

A letter is not a mark: it covers a band. With an example scale of A from 80 to 100 percent, B from 70 to 79, C from 60 to 69, D from 50 to 59 and F below, 15 out of 20 (75 percent) gives B, like 14 out of 20 (70 percent). The exact mark can no longer be recovered from the letter.

The letter scales of the English-speaking subsystem exams (GCE) give points to each letter; these points, reported by several sources, must be confirmed for each session. We found no official table of equivalence between marks out of 20 in the French-speaking subsystem and GCE letters.

A letter covers a band of marks: two students on 14 and 15.9 out of 20 may have the same letter.
Do not average letters: go through weighted points (GPA) or through the original marks.
Do not turn a letter back into a number to make an average: you invent a precision that does not exist.
In a school with two sections, one marked out of 20 and the other in letters, publish a written table of correspondence and apply it to everyone.

What Sahel EDU converts for you

Sahel EDU marks out of 5, 10, 20 or 100, with letters (A+ to F), grades or a GPA at the school’s choice. Each assessment keeps its own scale: a mark of 8 out of 10 enters an average out of 20 as 16. Averages are calculated on the scale of the class and displayed with their scale (“15.25 / 20”). Each recorded average keeps its scale, so that a later change does not distort it. Each assessment carries a weight, 1 by default.

The letter is read from a percentage: 15 out of 20 and 75 out of 100 give the same letter. The scales available include the Cameroonian one out of 20 with its grades, GCE scales (their points are to be confirmed by the school) and Arabic scales. These are marking scales, not national school systems: Sahel EDU creates no official equivalence between two systems. A school with sections (French-speaking, English-speaking, bilingual, Arabic) can give each one its own marking system and its own report card.

Frequently asked questions

How do I convert a mark out of 10 to a mark out of 20?

Multiply by 2: 7 out of 10 gives 14 out of 20. For a mark out of 5, multiply by 4.

How do I convert a mark out of 100 to a mark out of 20?

Divide by 5: 63 out of 100 gives 12.6 out of 20.

Should each converted mark be rounded?

No. Keep the decimals and round only the final average, otherwise the roundings add up.

Is a mark out of 20 compulsory in Cameroon?

In French-speaking secondary schools, a mark out of 20 remains the rule, including with the competency-based approach. For primary school, the official text sets neither the maximum mark nor the labels of the levels.

Can I try these conversions on my own classes?

Yes. The free trial lasts 30 days, with no commitment. The price is then negotiated with each school and can be read on the Pricing page.

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