Your one rep max (1RM) is the single heaviest weight you can lift for one repetition of a given exercise with proper form. It is the foundation of every serious strength program, and if you do not know yours, you are guessing every time you load the bar.
The good news: you do not actually need to grind out a maximal single to figure it out. Several research-backed formulas let you estimate your 1RM from a lighter set, and the results are surprisingly accurate. Here is how to do it, which formula to pick, and how to use the number once you have it.
What Is a One Rep Max and Why Does It Matter?
Your 1RM is more than a bragging number. It is a practical tool that unlocks percentage-based training, the method used by virtually every structured strength program from beginner linear progression to advanced periodization.
When a program tells you to squat at 80% for 5 sets of 3, that percentage refers to your 1RM. Without that reference point, you are picking weights based on feel, which works until it does not. Here is what knowing your 1RM actually gives you:
- Precision in programming. You can assign exact loads for strength, hypertrophy, and endurance work instead of guessing.
- Objective progress tracking. A 5 kg jump in your estimated 1RM over eight weeks tells you more than "the weight felt easier."
- Identifying weak points. Comparing your squat, bench, and deadlift 1RMs reveals imbalances between movement patterns and muscle groups.
- Autoregulation. On days you feel off, you can drop to a lower percentage and still train productively because you know what each percentage should feel like.
The Two Most Popular 1RM Formulas
Dozens of formulas exist, but two dominate the fitness world: the Epley formula and the Brzycki formula. Both take the same inputs (weight lifted and reps completed) and produce a 1RM estimate.
The Epley Formula
1RM = weight x (1 + reps / 30)
This is the most widely used formula in commercial gyms, fitness apps, and training literature. It uses a simple linear relationship and tends to produce slightly higher estimates, especially at lower rep ranges.
Example: You bench press 80 kg for 6 reps. 1RM = 80 x (1 + 6/30) = 80 x 1.2 = 96 kg
The Brzycki Formula
1RM = weight x (36 / (37 - reps))
The Brzycki formula uses an exponential curve and produces more conservative estimates. It is the preferred formula in research settings and has been validated by the NCAA for college athletes.
Example: Same bench press, 80 kg for 6 reps. 1RM = 80 x (36 / (37 - 6)) = 80 x (36/31) = 92.9 kg
Which Formula Should You Use?
The honest answer: it depends on the rep range you are testing with.
- 2-5 reps: Epley and the Wathen formula tend to be closest to actual 1RM based on powerlifting studies.
- 6-10 reps: Brzycki and Mayhew formulas excel here, with errors under 5% in research.
- At exactly 10 reps: Epley and Brzycki produce identical results.
- Above 10 reps: All formulas lose accuracy significantly. Avoid estimating from sets of 12 or more.
For most lifters, the Epley formula is the practical default. It is simple, widely referenced, and accurate enough for programming purposes. If you want a more conservative number for planning competition attempts, go with Brzycki.
How to Estimate Your 1RM Without Maxing Out
You do not need to load up a barbell and pray. Submaximal estimation is safer, faster, and nearly as accurate as direct testing. Research shows an intraclass correlation of 0.98-0.99 between estimated and actual 1RM values, and the injury rate for submaximal testing is less than 0.05 per 1,000 training hours.
Here is the protocol:
- Warm up thoroughly. Do 2-3 progressively heavier warm-up sets of the exercise you want to test.
- Pick a weight you can lift for 3-8 reps. This is the sweet spot for accuracy. Fewer than 3 reps gets too close to an actual max. More than 10 reps makes the estimate unreliable.
- Perform the set to technical failure (the point where one more rep would compromise your form, not absolute muscular failure).
- Record the weight and reps. Plug them into the Epley or Brzycki formula.
- Rest and retest if needed. If the set felt too easy or too hard, adjust the weight and try again after 3-5 minutes of rest.
A Quick Warning About Rep Range
The further you get from a true single, the less accurate any formula becomes. A set of 5 at 100 kg will give you a tighter estimate than a set of 15 at 60 kg, even though both might calculate to a similar 1RM. Stick to the 3-8 rep range for the best results.
When Should You Actually Test a True 1RM?
Direct 1RM testing has its place, but it is not for everyone. Research confirms that 1RM testing is safe when performed correctly, but there are important caveats.
Good candidates for direct testing:
- Intermediate to advanced lifters with solid technique
- Competitive powerlifters or weightlifters preparing for a meet
- Anyone who has been training consistently for at least 6-12 months
Stick with estimation if:
- You are a beginner (your nervous system may not handle true maximal loads yet, which means the number you get will underrepresent your potential anyway)
- You train alone without a spotter
- You have a history of joint issues or injuries
- You are in a clinical or rehabilitation setting
The American Council on Exercise specifically recommends estimated 1RM calculators for clients who may not be ready for maximal testing.
The One Rep Max Percentage Chart
Once you know your 1RM, this chart from the NSCA tells you how to translate it into training loads:
| % of 1RM | Expected Reps |
|---|---|
| 100% | 1 |
| 95% | 2 |
| 93% | 3 |
| 90% | 4 |
| 87% | 5 |
| 85% | 6 |
| 80% | 8 |
| 75% | 10 |
| 70% | 12 |
| 65% | 15 |
The general rule: each rep change corresponds to roughly a 2.5% shift in load. This is an approximation, not a law. Individual variation is significant, and some lifters can knock out 10 reps at a weight that others can barely do 7 with. Use the chart as a starting point and adjust based on your own performance.
How to Use Your 1RM for Different Training Goals
Different goals call for different percentages. Here is how to match your 1RM to your training objective:
Maximal Strength (85-100% of 1RM)
- 1-5 reps per set
- Long rest periods (3-5 minutes)
- This is pure neural and muscular strength work. Heavy, low volume, high intent.
Hypertrophy (65-85% of 1RM)
- 8-15 reps per set
- Moderate rest (60-120 seconds)
- The classic bodybuilding range. Enough load to create mechanical tension, enough reps to accumulate metabolic stress and volume.
Muscular Endurance (50-65% of 1RM)
- 15+ reps per set
- Short rest (30-60 seconds)
- Useful for conditioning phases, sport-specific endurance, or deload weeks.
Power (75-90% of 1RM)
- 1-5 reps per set, performed explosively
- Full rest (3-5 minutes)
- The focus here is bar speed, not grinding. If the rep slows down, the set is over.
A.S. Prilepin's analysis of thousands of elite weightlifters found that optimal strength work at 85-95% of 1RM involves 2-4 reps per set for a total of 10-20 reps per session. That is a useful guideline if you are building your own program.
How Often Should You Retest Your 1RM?
There is no need to retest every week. For most lifters, recalculating every 4-8 weeks is plenty. You can do this passively by simply noting your best set during normal training and running the numbers.
For example, if your estimated squat 1RM was 140 kg last month and you just hit 120 kg for 6 reps (which calculates to 144 kg), you have evidence of progress without ever touching a maximal single.
This is where a good training log becomes essential. If you are tracking your sets and reps consistently in an app like SILA, your estimated 1RM updates automatically as you log heavier or higher-rep sets. You get a running picture of your strength over time without dedicated testing sessions.
Common Mistakes When Calculating Your 1RM
Using sets above 10 reps. The formulas were not built for this and accuracy drops sharply. If you can only test with light weight, use a load that limits you to 8 reps or fewer.
Not going to true technical failure. If you stop at 6 reps but could have done 9, your estimate will be too low. The formulas assume the rep count represents your actual limit at that weight.
Testing when fatigued. Your 1RM estimate is only as good as the set you base it on. Test at the beginning of a session when you are fresh, not after 5 working sets.
Treating the number as gospel. Your 1RM fluctuates day to day based on sleep, nutrition, stress, and accumulated fatigue. Think of it as a useful reference point, not a fixed ceiling.
Ignoring individual variation. Lifters with more fast-twitch muscle fibers tend to have a bigger gap between their 1RM and their 10RM. Lifters with more slow-twitch fibers can grind out more reps at higher percentages. The standard charts are averages, not personal prescriptions.
Putting It All Together
Calculating your one rep max is one of the simplest things you can do to make your training more intentional. You do not need special equipment, a coach, or even a particularly hard workout. Just pick a weight, push it to technical failure in the 3-8 rep range, and plug the numbers into the Epley formula.
From there, you have a reference point for every set you do. Your warm-ups have purpose. Your working sets have precision. Your progress has a number attached to it.
Track it over time, recalculate it regularly, and watch the trend line move up. That is what real strength progress looks like.