One Rep Max (1RM) Calculator

This one rep max calculator estimates the maximum weight you can lift for a single repetition based on your submaximal lift data. Enter the weight and reps performed to calculate your 1RM using multiple validated formulas including Epley and Brzycki.

Calculate Your One Rep Max

Enter the weight you lifted and the number of reps you completed to estimate your one-rep max across multiple formulas.

Enter reps between 1 and 30. If reps = 1, the weight entered is your 1RM.

Frequently Asked Questions

What is a one rep max (1RM)?

A one rep max (1RM) is the maximum amount of weight you can lift for a single repetition with proper form. It is the gold standard for measuring absolute strength in a given exercise and is used to program training loads, track progress, and compare strength levels between individuals.

How do you calculate one rep max?

You can estimate your one rep max by performing a set with a lighter weight to near failure, then plugging the weight and reps into a formula. The most common is the Epley formula: 1RM = Weight x (1 + Reps / 30). Other formulas include Brzycki, Lombardi, Mayhew, and O'Conner, each using slightly different math to predict your max.

What is the Epley formula?

The Epley formula is 1RM = Weight x (1 + Reps / 30). It is one of the most widely used one rep max prediction equations due to its simplicity and reasonable accuracy for rep ranges of 1-10. For example, if you lift 200 lbs for 5 reps, your estimated 1RM is 200 x (1 + 5/30) = 233 lbs.

How accurate are 1RM calculators?

1RM calculators are most accurate when using rep ranges of 1-10. Accuracy decreases with higher rep counts because muscular endurance becomes a larger factor. Most formulas are accurate within 5-10% for trained lifters using low rep ranges. Using multiple formulas and averaging the results can improve the estimate.

Why is knowing your 1RM important?

Knowing your 1RM allows you to program training loads as percentages of your max, which is the foundation of periodized strength training. For example, hypertrophy work typically uses 65-75% of 1RM, strength work uses 80-90%, and peaking uses 90-100%. It also helps track progress and set realistic training goals.

How many reps should I use to estimate 1RM?

For the most accurate estimate, use a weight you can lift for 3-5 reps with good form. Rep ranges of 1-6 provide the most reliable predictions. As the rep count increases beyond 10, the estimate becomes less accurate because the formulas were validated primarily on lower rep ranges and fatigue patterns change.

What percentage of 1RM should I train at?

Training percentages depend on your goal. For maximum strength, train at 85-100% of 1RM for 1-5 reps. For muscle hypertrophy, use 65-80% for 6-12 reps. For muscular endurance, use 50-65% for 12-20 reps. For power development, use 50-70% with explosive movements. Most programs cycle through these ranges over time.

How to Calculate Your One Rep Max (1RM)

What is a One Rep Max (1RM)?

A one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It is widely considered the gold standard for measuring absolute strength in weight training and powerlifting.

Rather than attempting a true 1RM in the gym, which carries a higher risk of injury, lifters commonly use submaximal loads and rep counts to estimate their 1RM mathematically. This approach is safer and can be just as accurate for programming purposes.

How to Use This Calculator

  1. Enter the weight you lifted in pounds (lbs) or kilograms (kg) using the unit toggle.
  2. Enter the number of reps you completed (between 2 and 30). If you lifted for only 1 rep, the weight itself is your 1RM.
  3. Click "Calculate 1RM" to see your estimated one-rep max from five different formulas.
  4. Review the formula breakdown and the percentage-based training weight table to plan your workouts.

For the most accurate estimate, use a weight that allows you to complete between 2 and 10 reps. Estimates become less reliable beyond 10 reps.

1RM Formulas Explained

This calculator uses five well-established formulas from exercise science research. Each formula takes your weight and reps as input and produces a slightly different estimate. The calculator averages all five to give you a reliable overall prediction.

Epley Formula (Most Popular)

1RM = weight x (1 + reps / 30)

Developed by Boyd Epley, this is the most widely cited 1RM prediction equation and is used by the National Strength and Conditioning Association (NSCA).

Brzycki Formula

1RM = weight x 36 / (37 - reps)

Created by Matt Brzycki, this formula is particularly accurate for lower rep ranges (under 10 reps) and is commonly used in collegiate strength programs.

Lombardi Formula

1RM = weight x reps^0.10

A power-based formula that tends to produce slightly more conservative estimates compared to Epley and Brzycki.

Mayhew Formula

1RM = (100 x weight) / (52.2 + 41.9 x e^(-0.055 x reps))

Uses an exponential decay model. This formula was originally derived from bench press data and works well across a wide rep range.

O'Conner Formula

1RM = weight x (1 + 0.025 x reps)

A simple linear model that provides a quick estimate. It tends to produce lower predictions for higher rep ranges compared to other formulas.

Examples

Example 1: Bench Press

You bench press 185 lbs for 5 reps.

  • Epley: 185 x (1 + 5/30) = 215.8 lbs
  • Brzycki: 185 x 36 / (37 - 5) = 208.1 lbs
  • Lombardi: 185 x 5^0.10 = 216.2 lbs
  • Average across all formulas: approximately 210 lbs

Example 2: Squat

You squat 100 kg for 8 reps.

  • Epley: 100 x (1 + 8/30) = 126.7 kg
  • Brzycki: 100 x 36 / (37 - 8) = 124.1 kg
  • O'Conner: 100 x (1 + 0.025 x 8) = 120.0 kg
  • Average across all formulas: approximately 123.75 kg

Percentage-Based Training

Once you know your estimated 1RM, you can use percentage-based training to structure your workouts. Different percentages of your 1RM correspond to different training goals:

  • 90-100% of 1RM (1-3 reps): Maximal strength and neural adaptations. Used in peaking phases for powerlifting.
  • 80-90% of 1RM (3-6 reps): Strength-focused training. The backbone of most strength programs.
  • 70-80% of 1RM (7-12 reps): Hypertrophy (muscle growth). Ideal for bodybuilding-style training.
  • 60-70% of 1RM (12-20 reps): Muscular endurance and volume accumulation. Often used in conditioning or accessory work.

The training weight table in the calculator automatically rounds weights to the nearest 2.5 lbs or 1.25 kg so you can load a barbell with standard plates.

Use Cases

Strength Program Design

Coaches and athletes use 1RM estimates to prescribe training loads. Programs like Wendler 5/3/1, Starting Strength, and Juggernaut Method all rely on percentage-based programming derived from a 1RM.

Progress Tracking

By periodically recalculating your estimated 1RM, you can track strength gains over time without needing to test a true max every training cycle.

Competition Preparation

Powerlifters and weightlifters use 1RM estimates to plan their attempt selections for competition, ensuring they open at a manageable weight and build toward a personal record.

Rehabilitation and Return to Training

After an injury, a 1RM calculator helps determine safe working weights based on submaximal tests, allowing a gradual and controlled return to full training loads.

Tips and Best Practices

  1. Use a rep range of 2-10 for the most accurate estimate. Higher rep sets (15+) reduce prediction accuracy.
  2. Perform your test set with strict form and full range of motion for reliable results.
  3. Warm up properly before your test set to ensure peak performance without fatigue.
  4. Retest your estimated 1RM every 4-8 weeks to keep your training weights current.
  5. Remember that 1RM estimates are exercise-specific. A squat 1RM does not predict your deadlift 1RM.
  6. Consider averaging multiple formulas (as this calculator does) rather than relying on a single equation for a more robust estimate.
  7. Never attempt a true 1RM without a spotter or safety equipment in place.