Free calculator
One-rep max calculator
Work out your one-rep max without risking a maximal attempt. Enter the weight you lifted and how many reps you got, and you'll get your estimated 1RM along with the percentage table for programming your sets.
Your set
Your estimated 1RM
One-rep max
93.3kg
Your 1RM percentage table
The percentages update with the result above. The estimated reps come from inverting the same formula, so they're consistent with your own calculation rather than a generic chart.
| % of 1RM | Load | Estimated reps |
|---|
What a 1RM is
Your 1RM (one-rep max) is the heaviest weight you can lift once with good technique on a given exercise. It's the standard reference for measuring strength and, more importantly, for programming: nearly every training method expresses intensity as a percentage of 1RM.
Testing your true 1RM means a maximal attempt, with the technical risk and fatigue that come with it. That's why the usual approach is to estimate it from a submaximal set: you lift a weight you can move for several reps, and a formula extrapolates the max.
How it's calculated: the Epley formula
This calculator uses the Epley formula — the same one the Forge app uses to estimate your maxes from the sets you log:
1RM = weight × (1 + reps ÷ 30)
With 100 kg for 5 reps: 100 × (1 + 5 ÷ 30) = 116.7 kg. Other well-known formulas exist (Brzycki, Lombardi, Wathen) and they all produce very similar results at low rep ranges; the differences show up above 10-12 reps, where none of them are particularly accurate.
Using the percentages to train
The ranges commonly used in strength and hypertrophy training:
- 85-100 % · Maximal strength. Sets of 1 to 5 reps, long rests (3-5 min). Low volume, high intensity.
- 70-85 % · Hypertrophy. Sets of 6 to 12 reps, rests of 90 s to 3 min. This is where most useful volume accumulates.
- 50-70 % · Endurance and technique work. Sets of 12 to 20+ reps. Useful for learning the pattern, for accessories and for deload sets.
One practical note: your 1RM isn't a fixed number. It moves with accumulated fatigue, sleep, stress and the phase of the programme you're in. Recalculating it every 4-6 weeks is more useful than treating it as a permanent mark.
Limitations worth knowing
- Technique rules everything. If the last reps were done with broken form, the result overestimates your real max.
- It depends on the exercise. It works well on barbell compounds (squat, bench press, deadlift, overhead press). On isolation work or machines, the extrapolation is less reliable.
- More reps, more error. A set of 15 says more about your endurance than your maximal strength.
- Close to failure or it doesn't count. If you had 5 reps left in the tank, you're calculating the 1RM of a set you didn't do.
Frequently asked questions
Which 1RM formula is the most accurate?
None of them is accurate in absolute terms — they're all estimates. At 1 to 6 reps, Epley and Brzycki normally differ by less than 2-3 %, which is irrelevant for programming. What matters is always using the same formula so your numbers stay comparable to each other over time.
How often should I recalculate my 1RM?
Every 4-6 weeks, or at the end of a training block. If you log your sets you don't need a test at all: you can estimate it from your best set each week and watch the trend, which is more informative than a single data point.
Can I calculate a 1RM for pull-ups or dips?
Yes, but you have to add your bodyweight to the load. For a pull-up with 20 kg added at 75 kg bodyweight, the real system load is 95 kg. Calculate the 1RM on that figure and then subtract your bodyweight to find the added weight it corresponds to.
Is it safe to test my true 1RM?
With experience, solid technique, a proper warm-up and either a spotter or safety bars, a 1RM test is a legitimate tool. If you've been training less than a year or haven't fully mastered the lift, an estimate from a set of 3 to 5 reps gives you practically the same information without the risk.
Your 1RM, calculated for you
Forge estimates your one-rep max for every exercise automatically from each set you log, shows you the trend and adjusts your routine's progression accordingly. No charts, no spreadsheets.
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These calculators provide estimates for informational purposes and do not replace the judgement of a qualified training or health professional.