One Rep Max Calculator

Formula

Epley Formula: 1RM = w × (1 + r ÷ 30); Brzycki Formula: 1RM = w × 36 ÷ (37 − r)

w represents the weight lifted during the test set (in pounds or kilograms). r represents the exact number of successful, full-range repetitions completed (typically between 1 and 12). 1RM is the resulting estimated single-repetition maximum load.

Worked example

Weight lifted

100

Reps completed

5

• Estimated 1RM (Epley): 116.7
• Brzycki: 112.5
• 90% of 1RM: 105
• 80% of 1RM: 93.3
• 70% of 1RM: 81.7

What the One Rep Max Calculator Does

A one-rep max (1RM) represents the absolute ceiling of your strength on a given lift for a single, fully controlled repetition. While testing a true 1RM provides direct data, it places significant stress on the central nervous system, joints, and connective tissues.

This One Rep Max Calculator estimates your maximal capacity without requiring a high-risk maximal effort. By inputting the weight lifted and the clean repetitions completed (ideally between 1 and 12), the tool evaluates your performance using two of the most widely accepted predictive equations in sports science: the Epley and Brzycki formulas. It also derives key training percentages (90%, 80%, and 70%) to help you program your working sets.

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Step-by-Step Worked Example

To see how the calculations work, consider a lifter performing a heavy set of bench presses or squats:

• Weight lifted ($w$): 100 (kg or lb)
• Reps completed ($r$): 5

1. Epley Calculation

The Epley formula assumes each repetition adds roughly $1/30$th (3.33%) of the weight to your base capacity: $$\text{1RM} = w \times \left(1 + \frac{r}{30}\right)$$ $$\text{1RM} = 100 \times \left(1 + \frac{5}{30}\right) = 100 \times \left(1 + 0.1667\right) = 116.67$$ Rounded to one decimal place, the estimated 1RM is 116.7.

2. Brzycki Calculation

The Brzycki formula uses an inverse linear model based on 37 target points: $$\text{1RM} = w \times \frac{36}{37 - r}$$ $$\text{1RM} = 100 \times \frac{36}{37 - 5} = 100 \times \frac{36}{32} = 100 \times 1.125 = 112.5$$ The Brzycki estimate is 112.5.

3. Training Load Percentages (Based on Epley)

• 90% of 1RM: $116.67 \times 0.90 = 105.0$
• 80% of 1RM: $116.67 \times 0.80 = 93.3$
• 70% of 1RM: $116.67 \times 0.70 = 81.7$

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How to Interpret Your Results and Training Zones

Predicted maxes provide the foundation for percentage-based training cycles, such as linear periodization, block periodization, or standard 5/3/1 progressions. Here is how standard strength zones correlate to these outputs:

| Percentage of 1RM | Repetition Range | Primary Training Adaptation | | :--- | :--- | :--- | | 90% and above | 1–3 reps | Maximal neural drive, peak force production | | 80% – 89% | 4–7 reps | Strength building with secondary hypertrophy | | 70% – 79% | 8–12 reps | Muscle hypertrophy and structural work | | Sub-70% | 12+ reps | Muscular endurance and technical speed work |

If your estimated 1RM is 116.7, programming an 80% working block would mean assigning approximately 93.3 for sets of 5 to 6 repetitions.

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Practical Tips for Accurate Testing

1. Keep Reps Low: Test with a weight you can move for 3 to 6 reps. Predictions derived from 4 reps are far more reliable than predictions derived from 11 reps.
2. Demand Strict Form: Do not count repetitions where you shortened depth on a squat, bounced the barbell off your chest, or hyperextended your lumbar spine.
3. Use Consistent Rest Intervals: Take full 3-to-5-minute rest periods before your test set to ensure your phosphocreatine energy system fully recovers.
4. Apply a Training Max: In practical programming, many coaches multiply the estimated 1RM by 0.90 to establish a "training max." This ensures daily volume sets remain sustainable even on days when recovery is imperfect.

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When Not to Rely on 1RM Formulas

While submaximal formulas are mathematically sound, they have limitations:

• High Repetition Sets: Above 10 reps, anaerobic lactic threshold and cardiovascular fitness begin to dominate performance, making formulas overstate true single-rep strength.
• Beginners: Novice lifters lack the neuromuscular coordination required to display true maximal strength. A beginner's technical efficiency often breaks down long before true physiological failure occurs.
• Isolation Exercises: Bicep curls, lateral raises, and leg extensions place uneven shear forces on smaller joints and rarely follow linear multi-joint strength curves. Reserve 1RM tracking for major compound movements like the squat, bench press, deadlift, and overhead press.

Comparison

Scenario	Input	Result
Lower input	Weight lifted: 80	Estimated 1RM (Epley): 93.3
Base example	Weight lifted: 100	Estimated 1RM (Epley): 116.7
Higher input	Weight lifted: 120	Estimated 1RM (Epley): 140

Common mistakes

• Using high-repetition sets (over 10–12 reps), which drastically reduces formula accuracy due to localized muscular endurance.
• Counting partial reps or reps completed with hitching, bouncing, or spotter assistance.
• Testing compound movements like squats and deadlifts while fatigued from prior heavy training.
• Assuming an estimated 1RM instantly converts across different exercise variations (e.g., front squat vs. back squat).
• Failing to account for differences in equipment, such as barbell sleeve friction or machine pulley leverage.

Checklist

• Warm up thoroughly with progressive submaximal sets before testing.
• Choose a working weight you can lift for 2 to 10 repetitions with strict form.
• Record only complete repetitions performed through a full range of motion.
• Stop the set when technical form breaks down rather than reaching absolute failure.
• Keep weight units consistent across inputs (enter all pounds or all kilograms).
• Rest at least 3 to 5 minutes prior to any heavy assessment set.

Calculators Percentage Editorial Team

Calculator guides from the Calculators Percentage team. These introductory examples are educational, not professional advice.

Last reviewed: November 12, 2026

This tool provides mathematical estimates based on validated exercise science formulas and should not replace professional athletic coaching or medical clearance. Always prioritize safety, proper technique, and adequate spotting when lifting heavy weights.