1RM Calculator (with RIR/RPE)

What is a 1RM?

Your one-rep max (1RM) is the heaviest weight you can lift once with good technique. Programs use it to set loads, for example 3 × 5 at 80% of 1RM, and to track strength over time.

Testing a true max is tiring and, without a spotter or safety bars, risky. So most lifters estimate it from a hard set of 3 to 10 reps instead. The fewer the reps, the closer the estimate: above about 12 reps, endurance matters as much as strength, and the formulas drift apart.

What is RIR?

RIR means reps in reserve: how many more reps you could still have done with good form when you ended the set. RIR 0 is failure; RIR 2 means two more reps were possible.

Plans write a target such as 3 × 8–12 RIR 2: end each set with about two reps left. The sets are hard enough to build muscle and strength, and you keep enough in the tank for the next set and the next workout.

How to judge your RIR

Most people misjudge RIR by about one rep, more often in sets of 12 or more reps and far from failure. Beginners usually think they are closer to failure than they are. Your judgement improves with practice.

Watch the speed of the reps: when a rep clearly slows down despite full effort, you are usually at RIR 1–2. Now and then, take the last set of a safe exercise, such as a machine or dumbbell exercise, to failure and compare the result with your guess. Don't do this in heavy squats, bench presses or deadlifts without safety bars or a spotter.

RIR vs RPE

RPE (rating of perceived exertion) is the 1–10 effort scale popularized by powerlifting. For a set of reps both scales say the same thing: RPE = 10 − RIR. RIR 2 is RPE 8, RIR 0 is RPE 10, and a half step such as RPE 8.5 means "maybe two more reps, surely one".

Below RPE 6 (more than 4 reps in reserve) the effort is too far from failure to judge reliably, so the table, like the app, stops at RIR 4.

%1RM chart by reps and RIR

The chart shows what percentage of your 1RM you can lift for a given number of reps at a given RIR. The “With RIR/RPE”, “Weight for a plan” and “Top set and back-off” modes use it, and so does the app's RIR/RPE calculator.

The estimated 1RM (e1RM) in the app's history and charts is calculated differently: for a single rep it is the weight itself, for more reps the average of several formulas, as in the “1RM from a set” mode.

Why the two modes give different numbers

The "1RM from a set" mode assumes the set was taken to failure and averages six formulas (four from 10 reps), as the app's 1RM calculator does. The "With RIR/RPE" mode reads the RPE table: the percentage of your 1RM you can lift for each number of reps at each RPE. The app uses the same table in its RIR/RPE calculator.

Around 5 reps the two agree. At higher reps the table credits you with more: 100 kg × 10 to failure gives 131 kg by the formulas and 135 kg by the table. Neither is your true max. Pick one method, use it consistently and watch the trend. In the app, the estimated 1RM in your history and charts uses the formula average.

Starting weights for a training plan

In SmartWorkout's free plans, week 1 is a calibration week: every exercise starts at the bottom of its rep range with one rep more in reserve than the plan's target. The "Weight for a plan" mode turns a recent set into that weight, using the same table as the app.

No recent set? Start light, do the bottom of the range with clearly more reps left, and let week 1 show you where you are.

Exercise guides for the big three

The calculator works for any exercise with an external load. Technique, muscles worked and common mistakes of the lifts people test most often:

• Barbell Bench Press
• Barbell Squat
• Deadlift

Estimates, not a test

The results are estimates for planning your training. If you test a real 1RM, warm up well, use safety bars or a spotter, and stop when your technique breaks down. If you have an injury or a health condition, talk to a doctor or physiotherapist first.

Frequently asked questions