How to Estimate Your One Rep Max
How to work out your one rep max without testing it, which formula to use, and the percentage chart for programming from it.
Last updated: 1 July 2026
Overview
Your one rep max is the heaviest weight you can lift once with good technique. It is the reference point most strength programmes use to set working weights.
You rarely need to test it. Estimating it from a set you have already done is accurate enough for programming and costs nothing in fatigue or risk.
Quick Answer
You can estimate your one rep max from a set of repetitions using the Epley formula: 1RM = weight x (1 + reps divided by 30). Estimates are most accurate for sets of ten reps or fewer taken close to failure.
Key Points
- Estimates are accurate within a few percent for sets of 10 or fewer.
- The set has to be genuinely close to failure to be meaningful.
- Accuracy falls off badly above 10 reps.
- Estimate regularly, test rarely.
- Different formulas give slightly different answers; pick one and stay with it.
The two common formulas
Epley: 1RM = weight x (1 + reps / 30)
Brzycki: 1RM = weight x 36 / (37 - reps)
Worked example, 100kg for 5 reps:
| Formula | Calculation | Estimate |
|---|---|---|
| Epley | 100 x (1 + 5/30) | 116.7kg |
| Brzycki | 100 x 36 / 32 | 112.5kg |
They differ by a few kilograms. Epley tends to read slightly higher at moderate reps, Brzycki slightly lower. Neither is definitively better; consistency matters more than which one you choose.
Percentage chart
| Reps to failure | Approximate percentage of 1RM |
|---|---|
| 1 | 100 |
| 2 | 95 |
| 3 | 93 |
| 4 | 90 |
| 5 | 87 |
| 6 | 85 |
| 8 | 80 |
| 10 | 75 |
| 12 | 70 |
| 15 | 65 |
Reading it the other way: if you know your max, this tells you what to load for a target rep count. If you know a rep performance, it tells you your approximate max.
Setting training weights
Once you have an estimate, common training percentages are:
| Goal | Percentage of 1RM | Typical reps |
|---|---|---|
| Maximal strength | 85 to 95 | 1 to 5 |
| Strength and size | 75 to 85 | 5 to 8 |
| Hypertrophy | 65 to 80 | 8 to 15 |
| Muscular endurance | 50 to 65 | 15 plus |
| Deload | 55 to 65 | Normal reps |
Where estimates go wrong
| Problem | Effect |
|---|---|
| Set not near failure | Underestimates your max significantly |
| More than 10 reps | Error grows quickly with rep count |
| Different exercise | 1RM is specific to the lift |
| Technique degrading | Estimates a max you cannot safely produce |
| High rep endurance ability | Some people do many more reps at a percentage than the chart predicts |
That last one is real and individual. Some lifters can do twelve reps at 80 percent; others manage six. If the chart consistently misreads you, build your own from your own logs.
When to actually test
Testing a true max is worth doing occasionally if you compete or simply want to know.
| Consideration | Guidance |
|---|---|
| Frequency | Every 3 to 4 months at most |
| Preparation | After a deload, feeling fresh |
| Safety | Spotters, or a rack with pins set |
| Warm up | Ramp thoroughly, singles at 80, 88, 94 percent |
For everyone else, estimates from working sets are sufficient and considerably safer.
Common Mistakes
| Mistake | Why it causes problems | Better approach |
|---|---|---|
| Estimating from a 20 rep set | Formula error is large there | Use sets of 10 or fewer |
| Estimating from a submaximal set | Underestimates badly | Take the set close to failure |
| Testing maxes monthly | High fatigue cost, little benefit | Estimate instead |
| Applying one lift's max to another | 1RM is exercise specific | Estimate each lift separately |
| Switching formulas between sessions | Makes trends meaningless | Pick one and stay with it |
Frequently Asked Questions
How accurate are 1RM formulas?
Within roughly 5 percent for sets of five or fewer taken close to failure. Accuracy declines as reps rise.
Should I test my one rep max?
Only if you compete or specifically want to know. Estimating from working sets provides nearly the same information without the fatigue and risk.
Why do calculators give different numbers?
They use different formulas. Epley, Brzycki and others were derived from different data sets and produce slightly different curves.
Can I use the same percentage chart for every lift?
Roughly, but not exactly. Most people can do more reps at a given percentage on lower body lifts than on upper body lifts.
Sources
National Strength and Conditioning Association - https://www.nsca.com/
American College of Sports Medicine - https://acsm.org/