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

Most serious strength training 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 225 to 245 over three months, you know your programming is working. If it's been stuck at 225 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 225 lbs 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.

225 × (1 + 5/30) = 225 × 1.167 = 263 lbs

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.

225 × 36 ÷ (37 − 5) = 225 × 1.125 = 253 lbs

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.

225 × 5^0.10 = 225 × 1.175 = 264 lbs

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 estimates that sit in the middle of the pack across most rep ranges.

100 × 225 ÷ (52.2 + 41.9 × e^(−0.275)) = 262 lbs

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.

225 × (1 + 5/40) = 225 × 1.125 = 253 lbs

Wathan formula

1RM = (100 × weight) ÷ (48.8 + 53.8 × e^(−0.075 × reps))

Another exponential model, developed by Dan Wathan. Tends to track close to Epley and Lombardi at low reps. At higher reps it often produces the highest estimates of the six, making it the most aggressive formula.

100 × 225 ÷ (48.8 + 53.8 × e^(−0.375)) = 264 lbs

Where the formulas agree — and where they don't

At 2-5 reps, all six formulas produce estimates within a narrow band. That's the sweet spot for estimation. Above 10 reps, they start telling very different stories — Wathan and Brzycki push the estimate up while O'Conner stays conservative. The interactive chart below shows exactly how they diverge.

Averaging all six reduces the bias of any individual formula and gives you a more robust estimate. That's what our 1RM calculator does — plug in your weight and reps, and get the average across all six instantly, plus a full percentage breakdown table for programming.

How accurate are these estimates?

The formulas are most accurate in the 2 to 6 rep range. Here's why:

• 1 rep: No estimation needed — that's already your 1RM
• 2-6 reps: Formulas are highly reliable (within 2-5% for most lifters)
• 7-10 reps: Still useful, but accuracy starts to drop
• 10+ reps: Formulas diverge significantly as muscular endurance becomes a bigger factor

Pro tip: If you want the most accurate estimate, use a weight you can lift for exactly 3-5 reps with good form. This is the sweet spot where all six formulas converge.

Using your 1RM for training

Once you know your estimated 1RM, you can program intelligently using percentages:

For example, if your estimated squat 1RM is 315 lbs and your program calls for 5×5 at 80%, you'd load 252 lbs — round to 250 or 255 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:

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 junk number. The formulas diverge wildly above 10 reps because fatigue and muscular endurance confound the estimate. Stick to 2-6 reps for estimation.

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

Most lifters calculate their 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 225 for 5 today and 185 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. You also get personal record notifications across every rep range — not just your 1RM, but your best 3-rep, 5-rep, and 10-rep performances.

Key takeaways

• You rarely need to actually max out. Estimating from a 3-5 rep set is safer and just as useful for programming
• Average multiple formulas for the most reliable estimate — our 1RM calculator does this automatically
• Stick to 2-6 reps when estimating. Accuracy drops significantly 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.