How to calculate your one rep max (1RM)
In strength training, your one rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It's the number that underpins percentage-based programming, measures your absolute strength, and tells you whether you're actually getting stronger over time.
But here's the thing: you don't need to actually max out to know it. Estimation formulas let you derive your 1RM from a submaximal set, so you can program and track progress without ever loading a true max, unless you want to.
Why your 1RM matters
Many popular strength programs are built around percentages of your 1RM. When a program says "5 sets of 5 at 80%," it means 80% of your one rep max. Without knowing that number, you're guessing, and guessing means suboptimal training.
Your 1RM also serves as a benchmark. If your estimated bench press 1RM went from 100 kg to 110 kg over three months, you know your programming is working. If it's been stuck at 100 kg for six months, something needs to change.
Testing vs. estimating: which should you do?
Testing your 1RM means loading the bar and attempting the heaviest single you can complete. It's the definitive answer, but it comes with tradeoffs:
- High injury risk if you're not experienced
- Requires thorough warm-up and ideally a spotter
- Fatiguing, it can derail the rest of your training week
- Only gives you one data point on one day
Estimating your 1RM means performing a submaximal set and plugging the weight and reps into a formula. It's safer, faster, and gives you a reliable approximation.
Estimates give you two things without ever having to max out: a number you can plug into percentage-based programs, and a way to judge whether you're getting stronger over time. If you also want to test your true max, for a competition, a periodic strength test, or just to see what you can lift, go for it. But you don't have to.
RepCount does this automatically, it uses the Epley formula to estimate your 1RM from every set you log, so you can track your max strength over time without ever actually maxing out.
Comparing the 1RM estimation formulas
Sports scientists have developed multiple formulas to estimate your 1RM from submaximal work. Each was derived from different study populations and uses a different mathematical model, which is why they produce different results, especially at higher rep ranges. Here are the six most widely used and how they compare.
All examples below use 100 kg for 5 reps so you can compare the results directly.
Epley formula
1RM = weight × (1 + reps ÷ 30)
The most popular formula. Developed by Boyd Epley at the University of Nebraska, it uses a simple linear model where each additional rep adds a fixed percentage to the estimate. Tends to produce mid-range estimates at low reps and climbs steeply above 10 reps.
100 × (1 + 5/30) = 100 × 1.167 = 117 kg
Brzycki formula
1RM = weight × 36 ÷ (37 − reps)
Created by Matt Brzycki in 1993. Also linear, but uses a ratio model. Nearly identical to Epley at 2-5 reps, then produces slightly higher estimates at 8+ reps. Note that this formula breaks at 37 reps (division by zero), which is why most calculators cap input at 36.
100 × 36 ÷ (37 − 5) = 100 × 1.125 = 113 kg
Lombardi formula
1RM = weight × reps^0.10
Uses a power function instead of linear or exponential models. Produces results close to Epley at low reps but grows more slowly at higher reps, making it one of the more conservative formulas above 10 reps.
100 × 5^0.10 = 100 × 1.175 = 118 kg
Mayhew formula
1RM = (100 × weight) ÷ (52.2 + 41.9 × e^(−0.055 × reps))
Uses an exponential decay curve, which better models the non-linear relationship between reps and max strength. Produces the highest estimates of the six at low reps.
100 × 100 ÷ (52.2 + 41.9 × e^(−0.275)) = 119 kg
O'Conner formula
1RM = weight × (1 + reps ÷ 40)
Structurally identical to Epley but with 40 as the divisor instead of 30. This produces the most conservative estimates of all six formulas, useful as a lower-bound reference when you want to program on the safe side.
100 × (1 + 5/40) = 100 × 1.125 = 113 kg
Wathan formula
1RM = (100 × weight) ÷ (48.8 + 53.8 × e^(−0.075 × reps))
Another exponential model, developed by Dan Wathan. Tracks close to Epley and Lombardi at low reps and runs near the top of the pack in the 8 to 12 rep range, though Brzycki overtakes it beyond that.
100 × 100 ÷ (48.8 + 53.8 × e^(−0.375)) = 117 kg
Where the formulas agree, and where they don't
At 4-8 reps, all six formulas produce estimates within a narrow band, about 7 kg apart on a 100 kg set. That's their tightest comparison band, not proof that the estimates are closest to your true max. Below 4 reps the band widens again, because Mayhew runs high when the reps are very low. Above 10 reps, they start telling very different stories. Wathan and Brzycki push the estimate up while O'Conner stays conservative.
Averaging all six smooths out the differences between formulas and gives you a consensus estimate. It does not guarantee better accuracy against your true max. That's what our 1RM calculator reports, alongside every individual result and a full percentage breakdown table for programming.
How accurate are these estimates?
Formula agreement is not the same as accuracy against a tested 1RM. A study of bench press and leg press found that 5RM tests predicted measured 1RM better than 10RM or 20RM tests. A recent comparison in trained older adults also found that prediction error varied by exercise and formula.
The formulas themselves agree most closely in the 4 to 8 rep range. Here's how the rest of the range behaves:
- 1 rep: No estimation needed, that's already your 1RM
- 2-3 reps: Close to a true max, though the formulas themselves spread out a little here
- 4-8 reps: Estimates cluster tightly, within about 7 kg of each other on a 100 kg set
- 9-10 reps: Still useful, but the formulas start to separate
- 10+ reps: They diverge sharply as muscular endurance becomes a bigger factor
Practical tip: Use a challenging set of around 4-6 reps, performed with consistent technique and close to technical failure. Lower-rep sets generally predict 1RM better than high-rep sets, but the exact error still depends on the exercise and lifter.
Using your 1RM for training
Once you know your estimated 1RM, you can program intelligently using percentages:
| Percentage of 1RM | Typical reps | Training goal |
|---|---|---|
| 90-100% | 1-2 | Peaking / maximal strength |
| 85-90% | 3-4 | Strength |
| 75-85% | 5-8 | Strength & hypertrophy |
| 65-75% | 8-12 | Hypertrophy |
| 50-65% | 12-20+ | Muscular endurance |
For example, if your estimated squat 1RM is 140 kg and your program calls for 5×5 at 80%, you'd load 112 kg, round to 110 or 112.5 depending on available plates. Our plate calculator can help you figure out exactly which plates to load.
This removes guesswork from every session. No more wondering "is this heavy enough?" or "am I overreaching today?" The catch is that your 1RM isn't static, it shifts as you get stronger. A workout tracker that recalculates your estimated max from each session keeps your training percentages current without you having to think about it.
Strength standards: where do you stand?
Curious how your numbers compare? Here are common benchmarks for intermediate and advanced lifters:
| Exercise | Intermediate | Advanced |
|---|---|---|
| Bench Press | 1.25× body weight | 1.5-2× body weight |
| Squat | 1.5× body weight | 2×+ body weight |
| Deadlift | 2× body weight | 2.5-3× body weight |
| Overhead Press | 0.75× body weight | 1×+ body weight |
These vary significantly by age, sex, body weight, and training history. They're rough guidelines, not hard rules. Click any exercise above to estimate your max for that specific lift.
Common 1RM mistakes
Maxing out too often
Testing your true 1RM every week is counterproductive. It's fatiguing, increases injury risk, and steals time from productive training volume. Save true maxes for competition or periodic testing every 3-6 months.
Using high-rep sets to estimate
Doing a set of 15 and plugging it into a formula gives you a less dependable estimate. Above 10 reps the formulas spread out, and individual muscular endurance has more influence on the result. Use a lower-rep set when practical.
Ego lifting to hit a number
Your estimated 1RM is a tool for programming, not a scoreboard. Chasing a number by using bad form, cutting depth, or bouncing reps only gives you a meaningless estimate and a higher chance of injury.
Not tracking over time
A single 1RM estimate is a snapshot. The real value comes from tracking your estimated 1RM over weeks and months to see trends. Are you getting stronger? Plateauing? Losing ground?
This is where an app like RepCount shines, it calculates the top set for each exercise using the Epley formula, so you can compare strength progress across sessions regardless of whether you did 3 reps or 8.
How RepCount tracks your 1RM automatically
It's easy to calculate your 1RM once and forget about it. But your max changes as you train, and you want to know when it does.
RepCount uses the Epley formula to estimate your 1RM from every logged set, then identifies the top set for each exercise. Bench 100 kg for 5 today and 85 kg for 10 next week? Both get converted to an estimated max so you can compare them directly, your strength progress isn't hidden behind different rep ranges.
You get estimated 1RM charts that show this trend over time, per exercise, across months or years.
Key takeaways
- You rarely need to actually max out. A challenging low-rep set can estimate your 1RM without repeated max testing
- Compare more than one formula if you want a consensus. An average does not guarantee greater accuracy
- Use 4-8 reps when you want the six formulas to agree most closely. They spread out sharply above 10 reps
- Use your 1RM for percentage-based programming. It turns guesswork into a system
- Track your estimated 1RM over time. Trends matter more than any single number
Ready to calculate your max? Try our free 1RM calculator, or download RepCount to track your estimated 1RM automatically from every workout.
How the formulas compare
See how estimates diverge as reps increase. Enter your working weight to personalize the chart.
At 5 reps the six formulas sit about 7 kg apart. At 15 reps that gap is 33 kg. They all agree at 1 rep, where the estimate is simply the weight you lifted. The Epley line is highlighted because RepCount uses it on every logged set, not because it is universally more accurate.
Frequently asked questions
How do I calculate my one rep max without actually maxing out?
Use a 1RM estimation formula. Perform a challenging set of about 4-8 reps close to technical failure, then plug the weight and reps into a formula like Epley (weight × (1 + reps ÷ 30)) or Brzycki (weight × 36 ÷ (37 − reps)). This is where the six formulas in RepCount's free 1RM calculator agree most closely, but the result is still an estimate.
Which 1RM formula is the most accurate?
No single formula is universally most accurate. Epley and Brzycki are widely used and tend to agree closely in the 4-8 rep range. The best fit varies by exercise and individual; averaging several formulas gives a consensus estimate, not a guarantee of greater accuracy.
How often should I test my actual 1RM?
Most lifters only need to test a true 1RM for competition preparation or every 3-6 months for benchmarking. For regular training, estimated 1RM from submaximal sets is safer and more practical. RepCount automatically estimates your 1RM from every logged set using the Epley formula.
What is a good 1RM for bench press, squat, and deadlift?
Common intermediate benchmarks are 1.25× body weight for bench press, 1.5× for squat, and 2× for deadlift. Advanced lifters typically hit 1.5-2× for bench, 2×+ for squat, and 2.5-3× for deadlift. These vary by age, sex, and training history.
Is testing your one rep max dangerous?
A true 1RM attempt carries more risk than regular training, but it's safe when done properly: warm up thoroughly, use a spotter or safety pins, avoid grinding reps with bad form, and don't max out when fatigued. For most training purposes, estimating from submaximal sets is both safer and more practical.