Stronglifts 1RM calculator: How We Estimate Your One Rep Max

NOTE: This feature is currently only available on iOS (iPhone, iPad). We plan to add it to Android later too.

Stronglifts estimates your one repetition max or e1RM. It calculates this based on the weight you lifted for one to twelve reps, or even 5x5.

You can find your e1RM when you go to the progress tab in the app.

  1. Open Stronglifts
  2. Tap "Progress" at the bottom
  3. Tap an exercise
  4. Enable e1RM

Stronglifts e1RM progress graphs

How Stronglifts calculates your estimated one rep max

Stronglifts uses three values to determine your estimated one rep max:

  1. Weight lifted
  2. Reps done
  3. RPE

Your RPE is your rate of perceived exertion. It's a 1 to 10 scale. RPE 10 is an all-out effort: you couldn't have done another rep if you tried. The RPE gives us an idea of how hard a set was so we can better determine your e1RM.

For 5x5 straight sets, your RPE will usually be between 6-8. If you look at an RPE table, you'll find the matching percentage for 5 reps at RPE 6-8 is about 80%. This means that if you do 5x5 200lb, your e1RM would be about 245lb.

Stronglifts currently only has an RPE entry when setting your weights when you start a new program. It does not have an option to enter your RPE per set. We're considering adding this feature so your e1RM is more accurate (email us if you're interested).

For now, we're making assumptions to guess what your RPE is. The resulting e1RM is in most cases close enough. Here are some examples...

  • If you do 5x5 200lb, we assume that your RPE is 8. Your first set is most likely not RPE 9 or 10. If it was, you couldn't repeat it for four more sets of five sets. And so your e1RM would be about 246.5lb (5x200lb@8 RPE).
  • If you're supposed to do 5x5 200lb, but you fail reps and do 4/3/3/2/2 200lb, we assume RPE 10. If you couldn't do 5 reps, then you're probably lifting to failure. In this case your e1RM would be 224lb (4x200lb@10 RPE).
  • If you do 1x1 200lb, we assume that your RPE is 10 and so your e1RM is 200lb. We assume RPE 10 because if you only do one set, you're usually going to be make it count. And so if you do 1x10 200lb (one set of 10 reps), we also assume your RPE is 10. Your e1RM would then be 270.5lb.

Frequently Asked Questions

Why does the e1RM not show for more than 12 reps?

Your e1RM becomes less accurate when you log more than 12 reps.

We've had requests for extending the e1RM calculations to support up to 40 reps. But this would result in inaccurate and misleading estimates. If you tried to lift an e1RM based on what you did for 40 reps, you would most likely not be able to lift that e1M. This is because when you do a high number of reps, your muscles are working more on endurance rather than maximum strength. The e1RM formulas assume that the decrease in weight as reps increase is linear and primarily related to short-term muscle fatigue. But this is not the case with higher rep ranges. The maximum weight you can lift for one rep doesn't match your endurance capacity when you do 40 reps.

For this reason, if you log more than 12 reps, the e1RM value will show as NA.

If you have any questions or feedback, please contact us at: support@stronglifts.com

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