Free strength calculator
1RM Calculator
Estimate your one-rep max from any set. Enter the weight and reps you lifted — and how close to failure you were — and see your max across seven proven formulas, plus the right load for every rep count.
Sample numbers are filled in to show how the tool reads. Change any field to see your own max — the result appears as soon as you edit anything.
The load on the bar for your top set.
How many clean reps you completed with that weight.
If you stopped before failure, tell us roughly how many more reps you could have done. We add those before estimating — otherwise the max comes out too low. “All-out” means you couldn't have done another rep.
Edit any field above to see your estimated 1RM, the load for every rep count, and how you rank against strength standards.
Free. No signup. Works on your phone in the gym.
Estimates use established strength-science formulas. This is a training utility, not a prescription — never attempt a true 1RM without proper warm-up, a spotter or safeties, and the experience to bail safely.
How 1RM estimation works
Every 1RM formula is really a reps-to-failure equation. Strength and rep-endurance trade off in a predictable way: the more reps you can do with a weight, the lighter that weight is relative to your true max. A formula captures that curve, so if it knows the weight you lifted and how many reps you got, it can work backward to the single-rep weight at the top of the curve.
The catch is the word failure. These equations assume the set ended when you physically couldn't complete another rep. A set of 5 that you could have pushed to 7 isn't a true 5-rep max — it's a 7-rep max in disguise, and feeding in the raw 5 would lowball your real strength. That's why this calculator asks how many reps you had left and adds them back before doing the math.
The further you extrapolate, the more the formulas disagree and the looser the estimate gets. From a heavy double or triple they tend to cluster tightly; from a set of twelve they spread out, because local muscular endurance — which varies a lot between people and between exercises — starts to dominate. Use 2–5 reps when you can.
The seven formulas
There is no single “correct” 1RM equation. Each was derived from a different population and exercise, and validation studies — most famously LeSuer et al. (1997) on the bench, squat, and deadlift — find that the most accurate one shifts by lift, by sex, and by rep range. So this calculator computes all seven, headlines their average, and shows you the spread. A tight spread means the formulas agree and you can trust the number; a wide spread is a built-in uncertainty signal.
| Formula | Form | Character |
|---|---|---|
| Epley | w × (1 + r/30) | The most widely used. Straight-line model; reliable at low reps. |
| Brzycki | 36w / (37 − r) | Popular straight-line model. Lands cleanly at 10 reps = 75%. |
| Lander | 100w / (101.3 − 2.67123r) | The equation behind the familiar NSCA reps-to-percent chart. |
| Lombardi | w × r^0.10 | A power-curve model. Runs more conservative as reps climb. |
| Mayhew | 100w / (52.2 + 41.9·e^−0.055r) | A curved model from bench-press research. Often strong for bench. |
| O'Conner | w × (1 + 0.025r) | The gentlest of the set — the most conservative estimate. |
| Wathen | 100w / (48.8 + 53.8·e^−0.075r) | A curved model that grades well in studies, especially on squat. |
Here w is the weight lifted and r is the effective reps to failure. The exponential models (Mayhew, Wathen) use the natural exponential e. All seven are unit-invariant — the multiplier is the same whether you work in pounds or kilograms.
Reps in reserve: the detail most calculators miss
Most public 1RM calculators silently assume every set was taken to absolute failure. Almost nobody trains that way — and the assumption quietly biases the result. If you stop a set with reps left in the tank, those unused reps are real strength the formula never sees.
The fix is simple arithmetic: effective reps = completed reps + reps left. Five reps with two left becomes a seven-rep set before the formula runs. Concretely, with Epley: 100 kg × 5 taken to failure estimates 116.7 kg, but 100 kg × 5 with two reps left estimates from seven effective reps → 123.3 kg. Same set on paper, very different max — and the second one is closer to the truth if you genuinely had two reps left.
This is also why the tool stays in plain language. You don't need to know what RPE or RIR means — you just tell it whether you went all-out or had a rep or two left, and it handles the conversion. One honest answer about effort does more for accuracy than picking the “right” formula.
Turning your 1RM into training loads
The calculator runs the math in reverse too. Once it knows your max, it shows the load you'd expect to handle for any rep count — and the percentage of your 1RM that represents. This is the practical payoff: programs are written in percentages (“work up to 3 × 3 at 90%”), and the chart turns those into actual plates.
The familiar landmarks: a 2-rep max sits near 95% of your 1RM, a 5-rep max near 87%, a 10-rep max near 75%. Those are the rounded consensus values; individual formulas vary by a few points, which the chart blends into a single load per row.
One important caveat — these are all-out loads, the weight you could lift for exactly that many reps and no more. For most training you want to leave something in reserve, so your everyday working weight for a given rep target should sit a little below the chart value. The chart tells you the ceiling; good programming lives just under it.
How accurate are these estimates?
Good, within their limits. The validation literature is consistent on a few points. First, low reps win: Reynolds and colleagues found prediction was strongest from 5-rep tests and degraded steadily as the test moved to 10 and then 20 reps. Brzycki himself flagged that the relationship stops being linear much past ten reps.
Second, high correlation isn't the same as being unbiased. LeSuer's data correlated above 0.95 with measured maxes, yet every formula still significantly underestimated the deadlift — by roughly 9–14%. The lesson: an estimate can track your strength faithfully over time while sitting a little high or low in absolute terms, especially on the deadlift.
Third, the exercise matters more than the formula. A 2024 meta-regression across hundreds of studies found that the reps-to-percentage relationship barely budges with age, sex, or training status — but it does shift by exercise, with lifts like the leg press allowing more reps at a given percentage than the bench press. So treat the number as a well-calibrated estimate for the big barbell lifts, and as a rougher guide on machines and isolation work.
Common 1RM mistakes
- Counting reps that weren't really there. A grinding rep that barely moved, or a rep with a form breakdown, isn't a clean rep. Count only the reps you'd be happy to show a judge.
- Ignoring reps in reserve. Estimating from a set you stopped well short of failure, without telling the calculator, systematically underrates your max.
- Estimating from very high reps. A 1RM guessed from a set of fifteen is barely a guess. Endurance and pacing dominate that far out. Use a heavier set of 2–5.
- Treating the estimate as a guaranteed lift. An estimated 1RM is a planning number, not a green light to load the bar and send it. Work up gradually and respect the day.
- Chasing the “best” formula. The spread between formulas is usually smaller than the day-to-day variation in your own strength. The average across all seven is a more stable target than any single equation.
Methodology
This calculator implements seven established rep-to-max equations exactly as published — Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner, and Wathen. The headline estimate is the arithmetic mean of all seven; the spread is the range from the lowest to the highest. Reps in reserve are added to your completed reps to get the effective reps to failure that the equations consume.
A genuine single is treated as a tested max — when your effective reps come to one, the result is simply the weight you lifted, not an extrapolation. The reverse chart inverts each formula to find the load at a given rep count and reports the consensus, with each load's percentage of your 1RM.
The estimate is most reliable for compound barbell lifts in the 2–10 rep range, taken to a known effort. It diverges for very high-rep sets, isolation and machine movements, and lifts the underlying research never studied. This is a training tool, not a guarantee: never attempt a true one-rep max without a thorough warm-up, a spotter or safety bars, and the experience to bail on a missed rep.
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Exercise Library
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Browse exercisesFrequently asked questions
What is a one-rep max (1RM)?
Your one-rep max is the most weight you can lift for a single repetition with good form. It's the standard benchmark for maximal strength, and most programs prescribe working weights as a percentage of it. Because truly testing a 1RM is fatiguing and carries some risk, most lifters estimate it from a set of several reps instead.
How do you estimate a 1RM from a set?
You take the weight you lifted and the reps you got, and feed them into a rep-to-max formula. The more reps you do, the further the estimate has to reach, so accuracy is best at low reps. For example, Epley estimates 1RM as weight × (1 + reps ÷ 30): 100 kg × 5 reps → 100 × (1 + 5/30) = 116.7 kg.
Which 1RM formula is the most accurate?
There's no single winner. Validation work shows the best formula changes by exercise, sex, and rep range — Mayhew and Wathen often grade well on bench, Wathen on squat, and nearly every formula underestimates the deadlift. That's why this tool headlines the average of seven formulas and shows the full spread, rather than anointing one equation.
What if I didn't go all the way to failure?
Tell the calculator how many reps you had left. Every formula assumes your set ended at failure — where you couldn't do another rep. Stop with 2 in reserve and a 5-rep set is really worth a 7-rep set of effort; ignoring that makes the estimate too low. We add your reps-in-reserve to your completed reps before estimating.
How many reps should I use for the best estimate?
Two to five reps gives the most reliable estimate. Accuracy is highest in the low-rep range and softens past about ten reps, where muscular endurance and exercise choice start to matter more than maximal strength. A 3- or 5-rep set to a known effort is the sweet spot — heavy enough to be predictive, light enough to be safe.
How do I use the percentage chart?
Once you have a 1RM, the chart shows the load you'd expect for each rep count and what percentage of your max that is — roughly 95% for a 2-rep max, 87% for 5 reps, 75% for 10. Use it to set training weights. These are all-out loads, so in everyday training you'd usually stop a rep or two short.
Should I just test my real 1RM instead?
For most lifters, an estimate is safer and nearly as useful. A true test needs a full warm-up, a spotter or safety bars, and the experience to bail on a failed rep. Powerlifters peaking for a meet test under those conditions; most everyone else is better off estimating from a heavy set of 3–5 and re-checking every few weeks. The estimate doubles as a fatigue check, too — a lower estimate at the same weight and reps can signal you need more recovery.
Does it work for every exercise?
It works best for compound barbell lifts — squat, bench, deadlift, overhead press — which is what the underlying research studied. Isolation and machine movements fatigue differently, so a set of 10 on a leg press doesn't behave like a set of 10 on the bench. Treat accessory and machine estimates as rougher, and lean on lower rep counts there.
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