Estimate your 1RM from any reps × weight using five validated formulas, with a full %1RM table (50–100% in 5% steps) for programming sets and reps.
Built and maintained by Paul Clark, Redmoon Software · Checked against what this tool computes on
| %1RM | Weight | Suggested reps |
|---|
Epley: w × (1 + reps/30). Brzycki: w × 36 / (37 − reps). Lombardi: w × reps^0.10. O'Conner: w × (1 + 0.025 × reps). Wathan: 100 × w / (48.8 + 53.8 × e^(−0.075 × reps)).
The %1RM chart uses standard rep-range pairings (95% ≈ 2 reps, 85% ≈ 5 reps, 70% ≈ 10 reps, etc.).
The tool runs your weight and reps through five published rep-max equations: Epley, weight times 1 plus reps over 30; Brzycki, weight times 36 over 37 minus reps; Lombardi, weight times reps to the power 0.10; O'Conner, weight times 1 plus 0.025 times reps; and Wathan, 100 times weight over 48.8 plus 53.8 times e to the power minus 0.075 reps. The default Average (all) option runs all five and takes the mean, which smooths out any single equation's bias.
Reps is the input that matters. The help text puts the reliable window at 1 to 10 reps, warns that above 12 accuracy falls away, and the field itself refuses anything above 15. The formulas also disagree by rep count: at five reps with 100 kg, Brzycki returns 112.5 and Lombardi 117.5, but at ten reps Epley and Brzycki both land on exactly 133.3. Plate rounding defaults to the nearest 2.5 kg, with nearest 5 lb and no rounding as alternatives.
The unit dropdown is a label, not a conversion — switching from kg to lb changes the suffix on the output and nothing else, so enter your weight in the unit you intend to read back. The Lift dropdown is cosmetic too: all five formulas take only weight and reps, so bench and deadlift with identical inputs return identical estimates. Any rep-max equation is a population fit; a set taken well short of failure will always under-report your true single.
None consistently wins, which is why Average (all) is the default and averages all five. Brzycki tends to read conservatively at low reps, Lombardi and Wathan higher; they converge around ten reps, where Epley and Brzycki give exactly the same answer.
Between one and ten, and the set should be taken close to failure. The field accepts up to 15 reps but the on-page help flags anything past 12 as unreliable, because at high reps you are measuring muscular endurance more than maximal strength.
No. The Lift dropdown only labels the result box; every formula uses weight and reps alone. In practice the same reps-to-max relationship does not hold identically across lifts, so treat the output as lift-agnostic and adjust from your own training history.
It converts your estimated max into working weights from 100% down to 50% in 5% steps, each paired with a suggested rep range — 95% for doubles, 85% for fives, 70% for ten to twelve. Use it to set loads when a program prescribes percentages.
Because you cannot load 117.3 kg on a bar. Nearest 2.5 kg matches a pair of 1.25 kg plates and nearest 5 lb matches a pair of 2.5 lb plates. Rounding is applied to the estimate and to every row of the percentage chart.
Epley and Brzycki are the two estimates offered, and they were fitted to different populations decades apart. Below about five reps they agree closely enough that the choice barely matters. Above ten they diverge steadily, and by fifteen the gap is large enough to change what you would load.
The averaged option splits the difference, which is a reasonable default when you have no reason to prefer one. What none of them can do is extrapolate honestly from a set of twenty — that is well outside the range either was built for, and the result is a guess with a decimal point on it.
An estimate assumes the set was taken close to failure. A set of five with three left in reserve produces a max estimate well under the real one, so the input that matters most is how hard the set actually was rather than the numbers you type.
True maximal strength also varies day to day with sleep, food, stress and where you are in a training block — several percent either way is normal. Treat an estimate as a training tool for setting working weights, not as a figure to defend.
Exercise matters too: these formulas were derived largely on compound barbell lifts and travel poorly to isolation work, where fatigue accumulates differently.
The standard or formula behind this tool, so you can check it rather than take it on trust.
Epley, B. (1985). "Poundage Chart." Boyd Epley Workout, University of Nebraska.
One of the two formulas in common use. It and Brzycki agree closely at low rep counts and diverge above roughly ten reps.
Brzycki, M. (1993). "Strength testing: predicting a one-rep max from reps to fatigue." JOPERD, 64(1), 88–90.
The other common formula. A 1RM predicted from a set of fifteen is an extrapolation well past where either was fitted.
Barbell Plate Loading Calculator (kg / lb)
Plate math for any target weight, with available plate inventory, in kg or lb — for Olympic, women's and trap bars.
Wilks, DOTS & IPF GL Powerlifting Score Calculator
Compare powerlifting totals across weight classes with Wilks, DOTS and IPF GL coefficients.
Macros from Calories Calculator (P / F / C in g)
Calculate grams of protein, fat and carbs from any calorie target with keto, balanced and high-protein presets.
Heart Rate, FTP & Pace Training Zone Calculator
Generate training zones from threshold heart rate, FTP or threshold pace for running, cycling and rowing.
Running Pace Converter & Race Time Predictor
Convert running pace between min/km and min/mi and predict your 5K, 10K, half and full marathon times.
Cycling Power to Speed Calculator
Estimate cycling speed from watts using bike weight, gradient, wind and surface drag.
