One-Rep-Max Calculator
Compare seven established one-rep-max formulas from a recent working set. Select the average for a balanced estimate, or choose the formula you prefer.
Your selected one-rep-max estimate
117 kg
Average of all formulas from 100 kg × 5 reps.
| Training focus | % of 1RM | Suggested weight |
|---|
Formula comparison
Different formulas can produce slightly different results. The average is a useful default for most people; use a specific method if your coach or training plan calls for it.
| Formula | Estimated 1RM |
|---|
Use the estimate wisely
One-rep-max formulas are estimates, not guarantees. They become less reliable as repetitions rise, especially above 10. Prioritise good technique, warm up properly, and use a spotter or safeties when appropriate.
Turn any working weight into a complete warm-up ramp with per-side plate loading →
Worked example, start to finish
Take the default: 100 kg for 5 reps. Each formula answers the same question — what could one repetition weigh, given that you managed five — and they disagree by 6.5 kg:
| Formula | What it does with 100 × 5 | Estimate |
|---|---|---|
| Epley | 100 × (1 + 5/30) | 116.5 kg |
| Brzycki | 100 × 36 / (37 − 5) | 112.5 kg |
| Lombardi | 100 × 50.10 | 117.5 kg |
| Mayhew | 100 × 100 / (52.2 + 41.9 × e−0.055 × 5) | 119 kg |
| O'Connor | 100 × (1 + 0.025 × 5) | 112.5 kg |
| Wathan | 100 × 100 / (48.8 + 53.8 × e−0.075 × 5) | 116.5 kg |
| Landers | 100 × 100 / (101.3 − 2.67123 × 5) | 113.5 kg |
| Average | the seven results added and divided by seven | 115.5 kg |
Everything is rounded to the nearest half unit, because that is the granularity plates actually come in. A spread of 112.5–119 kg is normal and is the reason this page shows every formula rather than a single number: the average is the estimate to train against, the spread is your uncertainty.
That 115.5 kg then drives the training loads below — 104 kg at 90%, 92.5 kg at 80%, 81 kg at 70% and 69.5 kg at 60%. Each of those is a bar you have to load, so the loading guides and the plate chart cover the common numbers, and the plate calculator handles the awkward ones like 92.5 kg with the plates you own.
Where the estimate breaks down. At one rep every formula returns the weight you entered — there is nothing to extrapolate. Above about five reps they drift high, because a set of ten says as much about your conditioning and pain tolerance as about strength. The calculator accepts one to twenty reps; treat anything past ten as a rough guide, and use a sub-maximal single or double for the real number. If you are chasing strength numbers, a bar that bends under load and plates that slide are false friends — see the barbell guide and the plate guide before you buy, and the rack guide for the safety you need to miss a lift.
One-rep-max questions
Which 1RM formula is the most accurate? No single formula wins for everyone. Epley (weight × (1 + reps/30)) tends to read high above about five reps, Brzycki (weight × 36/(37 − reps)) reads low in the same range, and the exponential models (Mayhew, Wathan) flatten out sooner. This calculator shows all seven and the average, which is the most honest estimate.
How many reps should I use for a 1RM estimate? Between one and five. Every formula here returns exactly the weight you entered at one rep, and error grows with reps because sets taken near failure depend on conditioning as much as on strength.
Why are the results rounded to half a unit? Because plates come in fixed sizes. A 115.5 kg estimate is shown as 115.5, and the training loads it produces are the numbers you can actually build on a bar.
Is a one-rep max estimate the same as testing? No. An estimate is a training reference. Testing a true max is a skill and a fatigue cost of its own, which is why most programmes estimate from sub-maximal sets and only test occasionally.