About the One Rep Max Calculator
A free 1RM estimator that runs five validated formulas side by side — with a training-percentage table — so you can programme working weights without a risky max-out attempt.
What it is
The One Rep Max Calculator estimates the maximum weight you could lift for a single repetition (1RM) from a normal working set. Enter the weight you lifted and the number of clean reps you performed, and it applies five validated formulas — Epley, Brzycki, Lander, Lombardi, and O'Conner — showing each result side by side plus an average. It then generates a training-percentage table from 50% to 95% of that estimated 1RM so you can look up working weights for any training goal instantly.
Everything runs in your browser — no data is sent to a server, no account is required, and there are no limits on how often you use it.
Key features
Five validated formulas + average
Epley, Brzycki, Lander, Lombardi, and O'Conner are all shown side by side so you can see where they agree and where they diverge. The average reduces any single formula's bias.
Training-percentage table
50–95% of the average 1RM with use-notes for warm-up, hypertrophy, strength, and peaking. Updates instantly as you change inputs so you never need to calculate percentages manually.
kg and lb support
Toggle between kilograms and pounds freely. Conversion is handled internally so the formula results and percentage table always match the selected unit.
Per-lift labelling
Label the result as bench press, squat, deadlift, overhead press, barbell row, or any custom lift to keep results organised when testing multiple movements.
High-rep accuracy warning
The tool warns you when you enter more than 10 reps, where formula accuracy degrades. Reps are clamped to a maximum of 12 to prevent wildly unreliable estimates.
Instant, private, no sign-up
Results update as you type. Your inputs are never stored or sent anywhere. Open the page and use it — no account or setup needed.
The formulas
All five formulas take a submaximal weight (w) and rep count (r) and return an estimated 1RM. They were each derived from experimental data and are cited across sports science literature. When reps = 1 the calculator returns the entered weight directly, since that is by definition your observed maximum for that set.
Epley (1985)
w × (1 + r / 30) — one of the oldest and most cited. Tends to give slightly higher estimates at higher rep counts.
Brzycki (1993)
w ÷ (1.0278 − 0.0278 × r) — popular in powerlifting. Agrees closely with Epley at 2–6 reps and diverges above 10.
Lander (1985)
(100 × w) ÷ (101.3 − 2.67123 × r) — derived from a different dataset, generally falls between Epley and Brzycki.
Lombardi (1989)
w × r^0.10 — a power-based model; tends to give higher estimates than the linear formulas, especially at higher reps.
O'Conner et al. (1989)
w × (1 + 0.025 × r) — a conservative formula that tends to give lower estimates; useful as a lower bound.
Average of five
The mean of all five results. Using an average reduces the individual error of any one formula and is the basis for the training-percentage table.
Accuracy and limitations
Estimates are most reliable for sets of 2–6 reps performed close to failure with proper form. Accuracy decreases above 10 reps because the rep–max relationship becomes less predictable and more individual. The tool warns you when reps exceed 10 and clamps input to 12.
Individual factors — technique, muscle fibre composition, fatigue, and the specific exercise — all affect how close a formula estimate is to your true maximum on a given day. Use the estimate for programming reference, not as a number to chase recklessly.
1RM estimates are a general reference only — not medical advice. Results are most accurate from sets of 2–6 reps and become less reliable above 10 reps. Always warm up progressively before heavy lifting, use proper technique, and use a spotter for any near-maximal or heavy sets. Lift within your current ability. If you have a heart condition, injury, or any health concern, consult a physician before training at high intensity.
Estimate your one rep max now
Free, no sign-up required. Works on any device, instantly.
Open the 1RM Calculator