One Rep Max (1RM) Strength Calculator

1RM Estimation Guide

What should I know about 1RM Estimation Formulas?

Several validated formulas estimate 1RM from submaximal lifts: Brzycki: 1RM = weight × 36 / (37 − reps). Most widely used. Most accurate for 2-10 reps. Epley: 1RM = weight × (1 + reps/30). Simpler. Slightly higher estimates than Brzycki at higher reps. Lombardi: 1RM = weight × reps^0.10. Useful for very high rep ranges. Wathan: 1RM = weight × 100 / (48.8 + 53.8 × e^(-0.075 × reps)). Most complex but well-validated. Best practice: average 2-3 formulas. Estimates become less accurate above 10 reps, since the relationship between reps and load becomes less predictable at higher, more endurance-oriented rep ranges.

Why Reps in Reserve Matters?

1RM estimates assume the set was taken to technical failure (RIR 0). If you stopped with reps in reserve: actual 1RM is higher than estimate. Adjustment: count the set as if it was at failure. If you lifted 100kg × 8 with 2 RIR: equivalent to 10 reps at 100kg to failure. 1RM ≈ 100 × 36/27 = 133kg (using Brzycki for 10 reps). RIR-based RPE scale (Mike Tuchscherer): RPE 10 = no RIR (true failure). RPE 9.5 = could grind out half a rep. RPE 9 = 1 RIR. RPE 8 = 2 RIR. RPE 7 = 3 RIR. RPE 6 = 4-5 RIR. Most lifters overestimate their RPE early in a set and underestimate it toward the end, so using RIR alongside RPE gives a more objective cross-check.

What should I know about Training Percentages?

Standard percentages of 1RM for different training goals: 1 rep at 100% (true 1RM test). 2-3 reps at 90-93% (strength testing). 3-5 reps at 85-90% (max strength). 5-8 reps at 75-85% (strength + hypertrophy mix). 8-12 reps at 65-75% (hypertrophy primary). 12-15+ reps at 55-65% (endurance, hypertrophy). Below 55%: speed/power work or warm-up. Working sets typically 70-85% for general strength training. Powerlifting peaking blocks: progress to 85-92.5% in the final weeks before testing. Hypertrophy-focused training typically uses a broader 60-80% range across more total sets and reps, prioritising overall volume over pure maximal load.

What do I need to know about 1RM Testing Protocol?

When to test: end of training block. Adequately rested (3-7 days reduced training before test). Familiar with the lift. Warm-up protocol (example for bar squat with target 200kg): 1. Empty bar × 10. 2. 60kg × 5. 3. 100kg × 3. 4. 140kg × 2. 5. 170kg × 1. 6. 185kg × 1. 7. 200kg × 1 (target). 8. Optional: attempt 205-210kg if first attempt was easy. Rest 3-5 minutes between heavy attempts. Adequate spotters and safety equipment. Powerlifting competitions: standardised technique requirements. Practice the specific lift's technique at lighter loads well before attempting a true maximal test, since poor form under near-maximal weight significantly raises injury risk.