Modified Borg Scale CR10: The 0 to 10 Version

Two scales carry Gunnar Borg’s name and they are not the same instrument. The 6 to 20 scale was built to track heart rate; the CR10 was built to behave like a ratio, so that doubling the number means roughly doubling the felt intensity. That property is why the 0 to 10 version took over in lifting, intervals and team sport, where heart rate stops being a fair witness.

The CR10 anchors

Borg’s category-ratio scale starts at 0, nothing at all, and passes through extremely weak — the just-noticeable effort, marked 0.5 — then very weak, weak (light), moderate, somewhat strong, strong (heavy), very strong, very very strong (almost maximal), and finally 10, maximal. The 0.5 step is not decoration: it is what lets the bottom of the scale express a just-noticeable effort, which a scale that started at 1 could not do.

The wording is Borg’s and is licensed through Borg Perception — the Rehabilitation Measures Database notes a fee of up to $1,100 for large organizations requesting use of the scale — so the anchors are described here rather than reprinted as the administered form. The 6 to 20 scale covers the other version rating by rating.

The session version reads differently, and that is deliberate

If you have used a 0 to 10 scale to grade a whole workout, you probably used Carl Foster’s rewrite rather than Borg’s original. Foster and colleagues modified the verbal anchors “to reflect the American idiomatic English”, so light became easy and strong or severe became hard. Their version runs 0 for rest, 1 very very easy, 2 easy, 3 moderate, 4 somewhat hard, 5 hard, 7 very hard and 10 maximal — and ratings 6, 8 and 9 carry no descriptor at all, on purpose, so raters place them by feel between the labeled points.

That reworded scale is the input to the session RPE training load calculation, where a single rating for the whole session is multiplied by its length in minutes.

Don’t confuse it with lifting RPE

A third 0 to 10 scale circulates in strength training, and it measures something else entirely: repetitions in reserve. There, an RPE of 8 means you could have done two more reps with that load — a countable fact about the set, not a description of how strong the sensation was. The reps in reserve scale and the RPE to percentage chart work from that definition. Grading a heavy single as “very strong” on CR10 and calling it RPE 8 in a program are two different claims that happen to share a number.

Where the federal guidelines sit

U.S. public health guidance uses its own 0 to 10 ruler of relative effort — “sitting is 0 and the highest level of effort possible is 10” — placing moderate activity at 5 or 6 and vigorous at 7 or 8. It is not Borg’s CR10 and does not carry the ratio property, but for reading a public health recommendation it is the scale being referred to. The Borg RPE calculator converts a rating on the 6 to 20 scale into the same light, moderate and vigorous bands.