Strength

What is RIR in lifting? RPE versus reps in reserve

Reps in reserve (RIR) is how many more good reps you could have done when you stopped a set. RPE, rate of perceived exertion, describes the same effort from the other direction. Both say how hard a set was, and Fortior uses your answer to estimate your strength and suggest weights.

Updated October 24, 2026

What is RIR in lifting?

Reps in reserve counts the reps you had left when the set ended. If you stop at 8 reps and could have done 2 more with the same technique, that set was 8 reps at RIR 2. If you could not have done another rep, it was RIR 0, which means the set was taken to failure.

The idea is to describe effort in a way that works across exercises and weights. Two lifters can both do 8 reps at 100 kg, and one may have had 4 reps left while the other had none. Reps alone cannot tell those sets apart.

RPE vs RIR: how they convert

RPE is usually a scale from 1 to 10. For lifting sets, RPE and RIR are mirror images of each other:

Fortior's set rows ask for RIR in whole numbers, so subtract an RPE from 10 if that is how you think. Separately, the Finish Workout screen has an optional Session RPE from 1 to 10. That rating describes the whole workout, not any one set.

Zero versus blank in Fortior

A zero and an empty field mean different things, and Fortior keeps them apart in your history, in sync and in exports.

• 0 means the set was taken to failure.
• Blank means you did not track effort. The field shows a dash, your history reads "RIR —", and VoiceOver says "RIR not recorded".

Where a calculation needs a number, such as estimated strength and suggested weights, a blank counts as 2 reps in reserve. It is never treated as failure. Averages and effort trends leave blank sets out instead of counting them as zero. A blank can also never make a set a verified top set, the kind of set that teaches Fortior which formula suits you (see estimated one-rep max).

How to rate a set honestly

Rate the set right after you finish it, while you remember how the last reps felt.

• Count reps you could have done with the same technique. A rep that would have needed a bounce, a hitch or a shortened range of motion is not a rep in reserve.
• Be cautious on long sets. Many coaches find effort easier to judge on heavier, lower-rep sets than on sets of 15 or more, where guesses tend to be less reliable.
• Do not type 0 for "not sure". A zero says the set reached failure, and a set of 1 to 3 reps at zero is treated as especially informative. If you did not track it, leave it blank.
• Calibrate now and then. Occasionally take a safe set all the way to failure, on a machine or with a spotter, to see how your rating compares with what actually happens.
• Stay consistent. A steady habit matters more than a perfect one. Trends hold up when you rate every session the same way.

How Fortior uses your RIR

• Estimated strength. Reps plus RIR gives reps to failure, the input to your estimated one-rep max.
• Suggested weights. Each planned set has a target RIR. Fortior's default target is 2, and templates can hold a target of their own. See progressive overload and your next weight.
• Hard sets. A set counts toward weekly muscle volume when it has at least 5 reps and 3 or fewer in reserve. See training volume.
• Effort trends. Sets that keep coming in harder than their target are one of the signals behind a deload suggestion. Blank sets are left out.

Effort ratings are subjective, and the estimates built from them are educational. Fortior is not medical advice.