One Rep Max Calculator
Enter the weight and reps from any challenging set to estimate your one-rep max using five validated formulas. Get a full percentage chart for training loads from 50% to 95% of your 1RM.
reps
Enter your values above to see the results.
Tips & Notes
- ✓Use a 3–6 rep set for the most accurate 1RM estimate. Higher rep sets (10+) produce increasingly unreliable estimates because muscular endurance factors inflate the result.
- ✓The set you use to estimate 1RM should feel like you had 0–2 reps remaining — an RPE of 8–9. A set where you stopped early (RPE 6) will underestimate your true max.
- ✓Recalculate your 1RM every 4–8 weeks or whenever you hit a new personal record. Training with stale percentages means your loads are too light and progress stalls.
- ✓For compound lifts (squat, bench, deadlift), 1RM formulas are accurate to ±5–8%. For isolation exercises (bicep curls, leg extensions), reliability drops significantly — use RPE-based loading instead.
- ✓Never attempt a true 1RM without an experienced spotter for bench press and overhead press, and without a safety bar setup or experienced spotters for squats. Formula estimates eliminate most need for true 1RM testing.
Common Mistakes
- ✗Using a high-rep set (12–20 reps) to estimate 1RM — at high reps, the estimate inflates significantly because formula math does not account for the cardiovascular and endurance components of long sets.
- ✗Testing 1RM with poor form or after cumulative fatigue from a heavy training session — 1RM estimates should come from a fresh, well-warmed-up set with full technical control of the lift.
- ✗Applying the same 1RM percentage to isolation exercises as compound lifts — rep-to-max relationships differ significantly between muscle groups, and isolation exercises have less reliable 1RM prediction.
- ✗Not updating 1RM estimates as strength increases — a 3-month-old 1RM number leads to underloading, which slows progress; reassess at least monthly when making rapid strength gains.
- ✗Treating the average of five formulas as more accurate than each formula individually — the formulas are correlated (they use the same inputs) and averaging does not reduce uncertainty the way averaging independent measurements would.
One Rep Max Calculator Overview
One-rep max is the measuring stick of absolute strength. It tells you exactly where you are and exactly what loads to use in training — and it changes as you get stronger, so recalculating every 4–8 weeks keeps your programming accurate.
One-rep max estimation formulas:
Epley Formula (most widely used): 1RM = weight × (1 + reps ÷ 30) Brzycki Formula (most accurate for 1–10 reps): 1RM = weight × 36 ÷ (37 − reps)
EX: Bench press — 100 kg for 6 reps Epley: 100 × (1 + 6 ÷ 30) = 100 × 1.20 = 120 kg Brzycki: 100 × 36 ÷ (37 − 6) = 100 × 36 ÷ 31 = 116.1 kg O'Conner: 100 × (1 + 0.025 × 6) = 115.0 kg Average of five formulas: approximately 117–118 kg Training load at 75% (hypertrophy): 117 × 0.75 = 87.8 kg → use 87.5 kg for 8–12 reps
Epley and Brzycki formula comparison:
Lombardi Formula: 1RM = weight × reps^0.10 Wathen Formula: 1RM = 100 × weight ÷ (48.8 + 53.8 × e^(−0.075 × reps)) O'Conner Formula: 1RM = weight × (1 + 0.025 × reps) Accuracy rule: formulas are most reliable for reps 1–8. Above 10 reps, muscular endurance factors inflate the estimate — results become less predictive of true 1RM.
EX: Squat — 80 kg for 3 reps (close to true max) Epley: 80 × (1 + 3 ÷ 30) = 88.0 kg Brzycki: 80 × 36 ÷ 34 = 84.7 kg At 3 reps, all formulas agree within ~4 kg — high confidence estimate. EX: Squat — 60 kg for 15 reps (endurance set) Epley: 60 × (1 + 15 ÷ 30) = 90.0 kg — likely an overestimate of true 1RM Brzycki: 60 × 36 ÷ 22 = 98.2 kg — formula diverges significantly at high reps Use 3–6 rep sets for the most accurate 1RM estimates.
Major 1RM formula comparison:
| % of 1RM | Rep range | Primary training effect | Example: 1RM = 120 kg |
|---|---|---|---|
| 90–100% | 1–3 reps | Maximal strength, neural recruitment | 108–120 kg |
| 80–90% | 3–6 reps | Strength and power development | 96–108 kg |
| 70–80% | 6–12 reps | Hypertrophy (muscle size) | 84–96 kg |
| 60–70% | 12–20 reps | Hypertrophy and muscular endurance | 72–84 kg |
| 50–60% | 20–30+ reps | Muscular endurance, technique work | 60–72 kg |
Percentage of 1RM — rep range and training adaptation:
| Formula | Most accurate rep range | Known characteristic |
|---|---|---|
| Epley | 1–10 reps | Tends to slightly overestimate at higher reps |
| Brzycki | 1–10 reps | Most accurate for low rep sets (1–6); underestimates at 10+ |
| Lombardi | 1–8 reps | Produces highest estimates; may overestimate |
| O'Conner | 1–12 reps | Conservative estimate; good for beginners |
| Wathen | 1–12 reps | Exponential decay model; performs well across rep ranges |
The key to useful 1RM estimation is choosing the right test set: heavy enough to produce meaningful fatigue (you should not have been able to do 5 more reps), but not so heavy that technique breaks down. A 3–6 rep set at roughly 80–90% of your true max produces the most accurate formula estimates. If you are training with RPE (Rate of Perceived Exertion), an RPE 8–9 set of 3–5 reps gives excellent 1RM data. Recalculate your 1RM every 4–8 weeks or whenever you set a new performance record — programming based on stale 1RM estimates keeps training loads too light as strength develops.
Frequently Asked Questions
For sets of 1–6 reps, most 1RM formulas are accurate within 5–10% of true tested maximum for compound lifts in most individuals. Research comparing Epley and Brzycki to actual 1RMs found mean errors of 3–7% for squat and bench press. However, individual variation is substantial — some people have a muscle fiber composition (more slow-twitch) that allows them to sustain higher percentages of 1RM for more reps, causing formulas to overestimate their 1RM. Others are the opposite. Testing with a 3–5 rep set and using the formula as a programming baseline, then adjusting based on feel, gives the most practical result.
Strength standards vary significantly by body weight, sex, and training experience. General reference points for a 75 kg male: beginner bench press 1RM approximately 60–80 kg, intermediate 100–120 kg, advanced 140+ kg. For squat: beginner 80–100 kg, intermediate 120–150 kg, advanced 180+ kg. For deadlift: beginner 100–120 kg, intermediate 150–180 kg, advanced 220+ kg. Women typically have 1RMs approximately 60–70% of male standards at the same body weight. These are rough categories — individual genetic variation in tendon length, limb proportions, and muscle insertion points creates enormous natural variation in strength potential.
For most training programs, recalculating 1RM every 4–8 weeks is sufficient. In strength-focused blocks where significant progress is expected (beginner and intermediate lifters during a focused program), monthly updates keep training loads appropriate. Advanced lifters with slower strength gains may update quarterly. You can also recalculate whenever you set a personal record during training — if you complete 5 reps at a weight that your previous estimate suggested should be your 3-rep weight, your 1RM has increased. Never use the same 1RM number for more than 3 months if you are training consistently — the numbers drift meaningfully over that period.
For most lifters, estimated 1RM from a 3–5 rep set is a safer and equally useful programming basis as tested 1RM. True 1RM testing carries meaningful injury risk — particularly for upper body pressing movements without experienced spotters — and peak strength varies day to day by ±5–8% based on sleep, nutrition, hydration, and nervous system readiness. Building programming around estimated 1RM and adjusting based on RPE within sessions produces better long-term results than rigid adherence to percentages from an occasionally tested true max. Many elite powerlifters rarely test true 1RM outside of competition.
Each formula was derived from a different dataset of athletes performing different exercises. The Epley formula (1985) was originally derived from American football players; Brzycki was based on general strength training research; Lombardi uses a power law model; Wathen uses an exponential decay model. Because they were derived from different populations and regression methods, they diverge — particularly at higher rep counts. For sets of 3–5 reps, all five formulas typically agree within 3–5%. For sets of 10–15 reps, they can diverge by 10–15% or more. The divergence at high reps reflects genuine uncertainty about how endurance-based performance translates to maximal strength.
Yes, but with reduced accuracy. The formulas were developed primarily from barbell compound lift data (squat, bench press, deadlift, overhead press). For these movements, accuracy is highest. For dumbbell exercises, the free-weight stabilization demands change the rep-to-max relationship, and estimates tend to be less accurate. For machine exercises, the guided movement reduces stabilizer recruitment, producing a different rep-to-failure relationship. For isolation exercises (bicep curls, leg extensions), individual variation in muscle fiber type dominates the rep-to-max relationship more than for compound lifts, making 1RM estimates unreliable. For these exercises, RPE-based loading is generally more practical than percentage-based programming.