One Rep Max (1RM) Calculator
Estimate your one-rep max from the weight and reps you lifted.
Uses the Epley formula to calculate your maximum strength for any exercise.
Your one-rep max (1RM) is the maximum weight you can lift for exactly one complete repetition with proper form. Rather than risk injury testing it directly, most lifters estimate it from a submaximal set using a formula.
The Epley Formula:
1RM = Weight × (1 + Reps / 30)
The Brzycki Formula:
1RM = Weight × 36 / (37 − Reps)
The Lombardi Formula:
1RM = Weight × Reps^0.1
Worked Example:
You squat 120 kg for 6 reps.
- Epley: 120 × (1 + 6/30) = 120 × 1.2 = 144 kg
- Brzycki: 120 × 36 / (37 − 6) = 120 × 36/31 = 139 kg
- Lombardi: 120 × 6^0.1 = 120 × 1.196 = 143 kg
Average of three formulas: 142 kg — a reliable working estimate.
Training Percentages Based on 1RM:
| Goal | % of 1RM | Sets × Reps |
|---|---|---|
| Max strength | 90–100% | 1–3 × 1–3 |
| Strength | 80–90% | 3–5 × 3–5 |
| Hypertrophy | 67–80% | 3–5 × 6–12 |
| Muscular endurance | 50–67% | 2–3 × 15–20 |
1RM Standards by Lift (intermediate male lifter, ~80 kg bodyweight):
| Lift | Intermediate 1RM |
|---|---|
| Back squat | 120 kg |
| Bench press | 100 kg |
| Deadlift | 140 kg |
| Overhead press | 65 kg |
Practical Tips:
- Use sets of 3–5 reps for the most accurate 1RM estimates; accuracy drops significantly above 12 reps
- Retest every 6–8 weeks during a strength phase to keep training weights current
- The formula overestimates for very high rep sets (15+) because fatigue distorts the calculation
A fourth formula worth knowing: Mayhew
The Mayhew formula was developed specifically from bench-press data and tends to be the most accurate predictor for that lift:
1RM = 100 × Weight / (52.2 + 41.9 × e^(−0.055 × Reps))
For bench press testing, Mayhew typically agrees with measured 1RM within 2–3% across the 3–10 rep range. For other lifts, the difference between Epley, Brzycki, Lombardi, and Mayhew is usually under 5%; the average of all four is a safe working number.
Safety: never test 1RM cold
Directly testing your 1RM carries real injury risk. The estimation formulas above let you skip that risk entirely. If you do test directly:
- Use a spotter, always. For squats and bench, two spotters is better than one.
- Thorough warm-up: 5–10 minutes general cardio, then warm-up sets at 50%, 70%, 85%, and 95% of estimated 1RM before attempting the test.
- Take 3–5 days of rest before a true 1RM test; testing fatigued risks both an inaccurate result and an injury.
- Set up safety pins or rails on a power rack to your dump position.
- Trust the estimation formulas if any of the above isn’t in place.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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