One-Rep Max Calculator

What it does

Estimate your one-rep max (1RM) — the most weight you could lift for a single repetition — based on a recent set you actually performed (weight + rep count). The tool computes 1RM using four well-known formulas: Epley (1985, the most commonly cited), Brzycki (1998, similar to Epley but slightly different curve), Lander, and O'Conner. Each gives slightly different numbers; the calculator shows all four with an averaged result and percentage-of-1RM table for programming purposes.

Why estimate rather than actually max out: testing a true 1RM is physiologically demanding and risky (peak load on tendons, ligaments, technique breakdown at maximum weight). Most strength programs use 5RM or 10RM tests then estimate the 1RM, then prescribe training percentages off that estimate. Powerlifting competitions actually test 1RM, but in training contexts the estimation approach saves recovery time and reduces injury risk.

The percentage table (60-95% of estimated 1RM) drives standard strength programming: strength work targets 80-95% for 1-5 reps; hypertrophy targets 65-80% for 6-12 reps; endurance targets 50-65% for 12+ reps; power / explosive work uses lighter loads (50-70%) but trained at maximal velocity. Your calculated 1RM × these percentages gives the working weights for each rep range.

Important caveats: formulas are accurate for moderate rep ranges (2-10 reps); above 10 reps the estimates diverge significantly because the underlying assumption (linear strength-rep relationship) breaks down. Lift technique matters: a 5RM with form breakdown gives an inflated estimate. For best accuracy, test with 3-5 clean reps to failure on a compound lift you’re practiced at.

How to use it

1. Enter the weight you lifted and how many reps you completed with it. Best: a recent set taken to (or very near) failure with clean technique.
2. The tool returns 1RM estimates from four formulas (Epley, Brzycki, Lander, O'Conner) plus an averaged result.
3. Use the percentage table to plan upcoming workouts: 5×5 squats at 80% means 5 sets of 5 reps with 80% of your estimated 1RM.
4. Re-test every 4-8 weeks. As you get stronger, your 1RM rises; programming based on stale numbers becomes inaccurate.
5. If estimates diverge widely (Epley says 300, Brzycki says 280), trust the lower one for safety in programming.

When to use this tool

• Setting up a new strength program based on percentages.
• Tracking strength gains over time without testing actual 1RM regularly.
• Comparing strength across exercises (your bench 1RM vs squat 1RM gives a rough capacity ratio).
• Planning a peaking program for powerlifting competition (estimate from training, then test on meet day).

When not to use it

• Actual competitions or strength records — those test real 1RM. Estimates are training tools, not record-grade measurements.
• Very high rep ranges (15+) — formulas lose accuracy. Use rep-range-specific programming or actual heavier-weight tests.
• Olympic lifts (snatch, clean & jerk) — these are skill-limited, not strength-limited; 1RM estimation from a 5RM doesn't translate the same way as squat or deadlift.
• After a long break from training — your CNS won't be calibrated; the first session back will feel disproportionately hard. Re-base your 1RM after 2-3 weeks of consistent training.

Common use cases

• Verifying a number or output before passing it on
• Quick calculation during a typical workday
• Pre-decision sanity-check on inputs and outputs
• Educational use — demonstrating the underlying concept