One-Rep-Max Calculator
Your one-rep max (1RM) is the heaviest weight you could lift once with good form. You don't need to test it: lift any weight for 2–10 reps, enter both numbers below, and two well-validated formulas estimate your 1RM — plus the percentages to use for every rep range.
Estimate your one-rep max (1RM) from any set without grinding out a risky true max. Enter the weight you lifted and how many reps you hit, and this free calculator returns your estimated 1RM plus a full percentage table for programming your working weights.
Training weights by percentage
| % of 1RM | Weight | Est. reps |
|---|---|---|
| 100% | 115 kg | 1 |
| 95% | 110 kg | 2 |
| 90% | 102.5 kg | 4 |
| 85% | 97.5 kg | 6 |
| 80% | 92.5 kg | 8 |
| 75% | 85 kg | 10 |
| 70% | 80 kg | 12 |
| 67% | 77.5 kg | 15 |
Use these to program your working sets — e.g. hypertrophy work often sits around 70–80% of your 1RM.
How the estimate works
A one-rep max is the most weight you can lift once. Rather than testing it directly, you can estimate it from a sub-maximal set. This calculator combines the two most-cited formulas:
Epley: 1RM = weight × (1 + reps ÷ 30) Brzycki: 1RM = weight × 36 ÷ (37 − reps) Estimate = average of the two
The same estimated-1RM line appears on your progress charts in the app, so the strength trend you see there matches this tool.
Worked example
Say you bench press 100 kg for 5 reps. Epley gives 100 × (1 + 5 ÷ 30) ≈ 117 kg; Brzycki gives 100 × 36 ÷ 32 = 112.5 kg. The average — about 115 kg — is your estimated 1RM. At 80% (a typical hypertrophy weight) you would train with around 92 kg.
Using percentages to program
Training percentages let you dial intensity to your goal: heavy strength work at 85–95% of 1RM, muscle-building work at 70–80%, and lighter technique or back-off sets below 70%. The percentage table above turns your estimate into concrete weights, rounded to the nearest plate step.
Frequently asked questions
What is a one-rep max (1RM)?
Your one-rep max is the heaviest weight you can lift for a single repetition of an exercise with good form. It is the standard way to measure maximal strength and to set training percentages.
How is 1RM calculated from reps?
This calculator uses two well-known formulas. Epley: weight × (1 + reps ÷ 30). Brzycki: weight × 36 ÷ (37 − reps). It shows both and reports the average as your estimated 1RM.
How accurate are 1RM estimates?
Estimates are most reliable when the set is about 12 reps or fewer — the closer you are to a true max, the more accurate the number. Above roughly 12 reps, fatigue and endurance skew the result, so treat it as a rough guide.
How do I use the percentage table?
Once you know your estimated 1RM, multiply it by a percentage to pick working weights. Strength work often sits at 85–95%, hypertrophy around 70–80%, and technique or warm-up work below 70%. The table does this for you.
Do I need to actually lift a true max?
No. Testing a true 1RM is fatiguing and carries more injury risk. Estimating from a set of 3–8 solid reps gives you a safe, accurate enough number for programming.
Track your strength over time
SSS Workout Assistant logs every set and charts your estimated 1RM as it climbs — free.
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