The Last Step in Scoring a SUS Questionnaire
You've converted all 10 System Usability Scale items to their 0-4 scale (odd items: raw score minus 1; even items: 5 minus raw score) and summed them to a total of 34, out of a possible 0-40.
What's the final step to turn that sum into the standard 0-100 SUS score?
The correct answer is "Multiply the sum by 2.5."
Once all 10 items are converted onto the common 0-4 scale (so higher always means more usable, regardless of whether the original item was positively or negatively worded) and summed to a 0-40 total, the SUS formula multiplies that sum by 2.5 to produce the final 0-100 score. A sum of 34 becomes 34 × 2.5 = 85 — a strong result, well above the ~68 average.
The distractors misdescribe the arithmetic: SUS doesn't rescale by dividing the sum against the benchmark average (68 is used only for interpreting the final score, not for computing it); it isn't a simple base-10 rescale unrelated to the instrument's actual 0-40 range; and the final score is the sum of the 10 converted items, not their average — averaging would produce a 0-4 result, not 0-100.
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