Why we show a range, not just a number
Every sub-maximal 1RM formula is a regression fit to a specific population of lifters performing specific exercises. None of them is objectively “correct” for you. Presenting a single decimal-precision number would overstate how much confidence you should have in it. Instead, we calculate your estimate five different ways and show you the full spread — the tighter the range, the more you can trust the number.
How to use your training percentages
The table above turns your estimated max into a practical loading guide. Lower percentages (50-69%) with higher reps build muscular endurance and technique; the 70-89% range is the workhorse zone for strength and hypertrophy training; 90%+ is reserved for low-volume max-strength work and should be used sparingly to manage fatigue. Typical rep ranges are shown for each percentage, but individual rep tolerance varies — use them as a starting point, not a rule.
Frequently asked questions
How accurate is a 1RM calculator?
Sub-maximal formulas typically estimate within about 5-10% of a true tested max when the set is taken close to failure at 10 reps or fewer. Accuracy drops the higher the rep count gets, which is why we show a range across five formulas instead of a single number.
How many reps should I use for the most accurate estimate?
Reps between 1 and 8 give the tightest, most reliable estimates. Between 9 and 12 reps the range widens. Above 12 reps, treat the result as a rough guide only — fatigue and pacing start to distort every formula.
Should I just test my 1RM directly instead?
A supervised, properly warmed-up single-rep test is always more accurate than any formula. This calculator is most useful when a direct test isn't practical — for example between max-effort testing blocks — or as a quick sanity check on your current strength.
Why do the five formulas give different results?
Each formula (Epley, Brzycki, Lombardi, McGlothin, Wathen) is a regression fit to a different dataset of lifters and lifts. None is universally correct — they simply model the fatigue-to-load relationship slightly differently, which is exactly why we show their spread as a range rather than picking one.
How often should I retest my one-rep max?
For most lifters, every 6-12 weeks is enough to track meaningful strength changes without the fatigue cost of frequent maximal testing. Using this calculator from your heaviest working sets in between is a lower-fatigue way to track progress.