One Rep Max: 1RM Calculator solves a problem every lifter runs into eventually: you just hit a hard set of five and want to know what that means for your actual max, without testing it for real and risking a missed lift. Most people end up on a search results page hunting for a calculator that does not want an email address first. So we built Iron Max, a free one-rep max calculator that lives right here in your browser. Enter what you lifted and how many reps you got, and the estimate updates as you go, with a barbell that loads plates to match the number.
Work out your one-rep max
It opens with a working example already filled in: 100 kg for 5 reps. Drag the sliders or type your own numbers to make it yours.
How to use it
Set the weight you lifted and the number of reps you completed with the sliders, or type exact numbers into the fields above them. Switch the toggle at the top between kg and lb at any time; your numbers convert automatically. The big number in the middle is your estimated one-rep max, and the barbell below it loads plates live to visualize that load on a standard bar.
Scroll down for the percentage table: 95, 90, 85, 80, 75, 70, and 65 percent of your max, each converted into an actual weight. Lifters use this for programming, picking a working weight for a heavy triple or a lighter volume day without doing the math by hand. Tap “Save today’s estimate” to add today’s number to a short history, saved only on your device, so you can see whether your estimate is trending up over time. Nothing you enter leaves your browser, and your last inputs are there again the next time you open the page.
How it compares to One Rep Max: 1RM Calculator
Iron Max does one job: turn a weight and a rep count into an estimated one-rep max, instantly, plus a percentage table for programming, on anything with a browser. The full One Rep Max: 1RM Calculator app goes further. It typically keeps a running log of your lifts across sessions, tracks multiple exercises side by side, and builds a longer history of your strength progress than a browser tab saving a handful of dates ever will.
We kept the core loop: enter your numbers, watch the estimate and the barbell move together. We deliberately left out full workout logging and multi-exercise tracking, because a page you land on mid-search should hand you a number in a few seconds, not ask you to set up a training log first.
Our honest advice: use Iron Max when you want a quick estimate after a set, or when you are explaining the math behind a rep-max formula to a training partner without either of you installing anything. Install the full app when you are ready to track every lift across every session and want your numbers building into a real training history.
Get the full app
One Rep Max: 1RM Calculator is free on Android, built for logging lifts and tracking your estimated max across exercises and sessions over time.
Frequently asked questions
How is one-rep max calculated?
Iron Max averages two standard repetition-max formulas: Epley (weight times 1 plus reps divided by 30) and Brzycki (weight times 36 divided by 37 minus reps). Both are widely used in strength training to estimate a max from a sub-maximal set, and averaging them smooths out the spots where either formula alone tends to run a little high or low.
How accurate is a one-rep max calculator?
It gets you close, not exact. Estimates from any repetition-max formula are most reliable at 10 reps or fewer, and accuracy drops the higher the rep count goes, since the math starts extrapolating further from a true single effort. Treat the number as a solid planning estimate, not a guaranteed number you will hit on your first attempt.
Can I use this for any lift?
Yes. The formula only needs the weight you lifted and the reps you completed, so it works for squats, bench press, deadlifts, or any barbell lift where you want an estimated max. The barbell visual is a generic illustration, not tied to a specific exercise.
Does it work offline and is it free?
Yes to both. It is completely free with no signup, and once the page has loaded it keeps working without a connection. Your last inputs and your saved history stay in your browser’s local storage on your device only.
Is this the official One Rep Max: 1RM Calculator app?
No. Iron Max is an original tool we built, inspired by the one-rep-max problem that One Rep Max: 1RM Calculator solves. It is not affiliated with, endorsed by, or connected to its developer. If you want full lift logging and a running max history, get the official app from the store links above.
