🏋️ One-Rep Max (1RM) Calculator
Estimate your one-rep max from any submaximal set using both the Epley and Brzycki formulas side by side, plus a training percentage chart.
Entering kilograms works exactly the same way — both formulas just multiply weight by a rep-based factor, so every result below comes out in whatever unit you typed in.
Training percentage chart
Based on the 212.0 average estimate above. The rounded column snaps to the nearest 5 lbs, since that is what most gym plates actually let you load.
| % of 1RM | Exact weight | Rounded to nearest 5 |
|---|---|---|
| 50% | 106.0 | 105 |
| 60% | 127.2 | 125 |
| 70% | 148.4 | 150 |
| 80% | 169.6 | 170 |
| 90% | 190.8 | 190 |
| 95% | 201.4 | 200 |
| 100% | 212.0 | 210 |
What One-Rep Max (1RM) Calculator Does
A one-rep max is, almost by definition, a number most lifters do not want to actually test — a true 1RM attempt carries real injury risk and requires a level of warm-up and technical readiness that most gym sessions are not built around. What gets used instead is an estimate: lift a weight for several reps short of failure, and use the relationship between weight and reps-to-failure to project what a single maximal rep would look like.
The honest complication, which most single-formula calculators skip past, is that this relationship has been modeled more than one way, and the different models do not always agree. This tool runs the set through two of the most widely used formulas — Epley and Brzycki — and reports both, plus how far apart they land, instead of presenting one number as if it were an exact measurement. When the two agree closely, that is itself useful information: it means the estimate is probably reasonably stable for that rep range.
The training-percentage table exists because a 1RM estimate is rarely the point on its own — it is almost always step one of picking work-set weights for a training program, so this tool carries the estimate straight through to the percentages a lifter would actually load onto a bar.
How to Use One-Rep Max (1RM) Calculator
- Choose the lift and enter the weight you lifted and how many reps you completed
- Compare the Epley and Brzycki estimates and their spread
- Use the training percentage chart to plan work sets off the estimated max
Formula Used by One-Rep Max (1RM) Calculator
Epley formula
1RM = weight × (1 + reps ÷ 30)
Worked example
185 lbs for 5 reps.
- 1 + 5 ÷ 30 = 1.1667
- 185 × 1.1667 = 215.83
Result: 215.8 lbs — confirmed in node -e before publishing.
Brzycki formula
1RM = weight × 36 ÷ (37 − reps)
Worked example
The same set: 185 lbs for 5 reps.
- 37 − 5 = 32
- 36 ÷ 32 = 1.125
- 185 × 1.125 = 208.125
Result: 208.1 lbs — about 3.5% below the Epley estimate for the same set, illustrating the real spread between the two formulas even at a moderate rep count.
Training percentage from the estimate
Work-set weight = estimated 1RM × target percentage
Worked example
An average estimate of 211.98 lbs (from the two formulas above), at 80% for a work set.
- 211.98 × 0.80 = 169.58
- Rounded to the nearest 5 lbs (the smallest plate increment most gyms load): 170
Result: ≈170 lbs for an 80% work set — verified in node -e alongside the rest of the percentage table.
Training percentages against a 200 lb one-rep max
A commonly published percentage-of-1RM chart (NSCA), applied to an example 200 lb max so the weights are concrete. Scale proportionally to your own estimate.
| Target reps | % of 1RM | Weight (200 lb max) |
|---|---|---|
| 1 | 100% | 200 lb |
| 2 | 95% | 190 lb |
| 3 | 93% | 186 lb |
| 4 | 90% | 180 lb |
| 5 | 87% | 174 lb |
| 6 | 85% | 170 lb |
| 8 | 80% | 160 lb |
| 10 | 75% | 150 lb |
| 12 | 67% | 134 lb |
How to Read Your Result
Why the estimates diverge more at higher reps
Both formulas assume the weight-versus-reps relationship follows a consistent shape, but past roughly 10 reps a set starts to test muscular endurance as much as maximal strength, and the two models' assumptions no longer track each other as closely. That divergence is real, not a bug in either formula — it is why this tool flags any set over 10 reps as a rough ballpark.
Neither formula is a substitute for a real test in every context
These are statistical estimates fit to average results across many lifters; an individual's actual 1RM can differ meaningfully, especially at the extremes of training experience. Treat the output as a planning number, not a promise.
Use the percentage table as a starting point, not a fixed prescription
The reps-to-percentage relationship above is itself an average, exactly like the two 1RM formulas — a lifter who is unusually strength- or endurance-biased for their level will find their own numbers sit a little off the chart in one direction. Treat both this table and the 1RM estimate as a starting point to adjust from set to set, not a fixed prescription.
Limitations & Accuracy Notes
- Both formulas assume the set was taken close to failure with good technique; a set stopped early with reps clearly left in the tank will underestimate the true 1RM.
- Accuracy degrades at higher rep counts — this tool caps input at 20 reps and visibly flags anything over 10 as a rough estimate rather than a number to load onto a bar.
- Does not adjust for exercise, limb length, or technique differences between lifters; the same formulas are applied regardless of which lift is selected.
- The percentage-of-1RM table is itself a population average and will not match every lifter's actual strength curve exactly.
Frequently Asked Questions
How is one-rep max calculated from fewer reps?
Why do Epley and Brzycki give different numbers?
Does this work in kilograms?
Why is there a rep limit?
References & Further Reading
- ExRx.net — Predicting One-Rep Max — States the Brzycki formula and the Baechle/Earle/Wathen (NSCA) percentage-of-1RM-by-reps chart the training-percentage table above is drawn from — verified against this live page