One Rep Max Calculator: Free 1RM Tool
Calculate your one rep max (1RM) in seconds with IRON's free calculator. Enter the weight lifted and reps performed to get a precise estimate of your max based on the three most trusted scientific formulas used in powerlifting, bodybuilding, and athletic training. No sign-up required.
One Rep Max Percentage Chart
This chart shows the relationship between reps, percentage of your one rep max, and training zone. If you've calculated your 1RM above, you'll also see the exact weight in kg for each percentage.
| REPS | % 1RM | ZONE |
|---|---|---|
| 1 | 100% | Strength |
| 2 | 97% | Strength |
| 3 | 93% | Strength |
| 4 | 90% | Strength |
| 5 | 87% | Strength |
| 6 | 83% | Hypertrophy |
| 7 | 80% | Hypertrophy |
| 8 | 77% | Hypertrophy |
| 9 | 75% | Hypertrophy |
| 10 | 73% | Hypertrophy |
| 12 | 67% | Hypertrophy |
| 15 | 65% | Endurance |
| 20 | 60% | Endurance |
| 25 | 55% | Endurance |
| 30 | 50% | Endurance |
STRENGTH
1-5 reps
85-100% 1RM
3-5 min rest
The max strength range focuses on heavy loads with few reps. Ideal for increasing your max on compound lifts like squat, bench, and deadlift.
HYPERTROPHY
6-12 reps
65-85% 1RM
60-90s rest
The hypertrophy range is the most common for building muscle mass. It combines good mechanical tension with sufficient volume to maximize growth.
ENDURANCE
12-20+ reps
50-65% 1RM
30-60s rest
The muscular endurance range uses lighter loads with high reps. It improves work capacity and stamina under load.
What Is the One Rep Max (1RM)?
The one rep max, or 1RM (One Repetition Maximum), is the maximum weight you can lift for a single repetition with proper form. It's the fundamental parameter for programming any gym training: all working loads, load percentages, and progression over time are based on this number.
Knowing your 1RM lets you set precise loads for each goal — max strength, hypertrophy, or muscular endurance — eliminating guesswork. If you don't know your max, you're essentially picking weights at random: you might train too light (no progress) or too heavy (injury risk).
Calculating your 1RM is useful for all athletes, from beginner to advanced, and for all compound and isolation exercises: bench press, squat, deadlift, overhead press, curls, and pull-ups. The most effective training programs — like Wendler 5/3/1, Starting Strength, and GZCL — are built entirely on 1RM percentages.
How to Calculate Your One Rep Max
Testing your max directly — loading the bar to the limit and attempting a single — is risky without a spotter and without experience. The safest and most practical method is using a calculator based on validated scientific formulas: lift a submaximal weight for multiple reps and the formula estimates your 1RM with a 5-8% margin of error.
Brzycki Formula
Published in 1993, it's the most widely used formula in powerlifting. Extremely accurate for sets of 1-10 reps, tends to slightly underestimate with more than 10 reps.
1RM = Weight × (36 / (37 - Reps))Epley Formula
Developed by Boyd Epley, it's the NSCA's reference formula. Reliable up to 15 reps, tends to slightly overestimate with very heavy loads (1-3 reps).
1RM = Weight × (1 + 0.0333 × Reps)Lombardi Formula
A power-based formula that provides balanced estimates across the full rep spectrum. Particularly useful as a third estimate to triangulate the result alongside Brzycki and Epley.
1RM = Weight × Reps^0.10Note: all formulas lose accuracy beyond 10 reps. For a reliable estimate, use a weight you can lift for 3-8 reps.
Want to track your max over time?
IRON records every PR automatically and calculates your 1RM every workout.
How to Use Your One Rep Max Result
Once you've calculated your 1RM, you can program your training scientifically using load percentages. Each rep range corresponds to a percentage of your max and produces a different physiological adaptation: neural strength, muscular hypertrophy, or metabolic endurance.
Practical example: if your bench press max is 100 kg, for hypertrophy work (6-12 reps) you'll use loads between 65 and 85 kg. For max strength (1-5 reps at 85-100%), you'll work between 85 and 100 kg. For endurance (12-20 reps), you'll use 50-65 kg. These ranges are the foundation of every serious training program — from Wendler 5/3/1 to GZCL to classic bodybuilding splits.
Recalculate your max every 4-6 weeks to update your working loads. As you progress, your 1RM increases and working loads must follow. Without periodic updates, you risk training with weights that are too light, slowing your gains.
Training Zones & 1RM Percentages
Knowing your one rep max lets you program training across three key zones: maximal strength, hypertrophy, and muscular endurance. Each zone has a specific intensity range calculated from your 1RM percentage.
Common 1RM Calculation Mistakes
Using too many reps
Formulas are designed for sets of 1-10 reps. Beyond 10, factors like cardiovascular endurance and lactate threshold distort the estimate upward. Always use a weight you can lift for 3-8 reps for the most accurate result.
Not accounting for accumulated fatigue
If you estimate your max at the end of a workout after 10 sets of squats, the result will be significantly underestimated. For a reliable estimate, test at the start of your session after a proper warm-up but before heavy working sets.
Confusing technical and true max
Your technical max is the heaviest weight you can lift with perfect form and full ROM. Your true max might be higher, but with compromised technique and elevated injury risk. For training programming, always use your technical max.
Not retesting periodically
Your 1RM changes over time — it can increase with consistent training or decrease during periods of inactivity. Recalculating every 4-6 weeks ensures your working loads remain challenging and progressive, avoiding both undertraining and overreaching.
One Rep Max by Exercise
Your 1RM varies dramatically from exercise to exercise. An intermediate lifter might have a 100 kg bench press, 140 kg squat, and 180 kg deadlift. These differences depend on the biomechanics of the movement, the muscle mass involved, and the mechanical leverage of the exercise.
The three fundamental powerlifting exercises — bench press, barbell squat, and deadlift — are where 1RM has the most practical relevance. But the calculation is also useful for overhead press, rows, barbell curls, and any movement with progressive overload. Each exercise has its own strength standards relative to body weight.
Dedicated pages with exercise-specific strength tables and experience levels coming soon.
One Rep Max Calculator FAQ
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