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One Rep Max (1RM) Calculator

Estimate your 1RM via Epley, Brzycki, and Lombardi formulas. Percentage chart for training loads.

One-Rep Max Calculator

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

Weight Lifted

Reps Performed

Between 1 and 30 reps

Unit

Understanding Your One-Rep Max (1RM)

Your one-rep max 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 and serves as the foundation for percentage-based training programs used by powerlifters, strength coaches, and recreational athletes alike.

How 1RM Formulas Work

Directly testing your 1RM requires a spotter, proper warm-up, and carries some injury risk — especially for beginners. Estimation formulas let you predict your max from a submaximal set. This calculator uses three widely validated formulas:

Epley (1985): One of the most popular formulas, calculated as weight × (1 + reps/30). It tends to be slightly more accurate for higher rep ranges (6–10).
Brzycki (1993): Uses the formula weight × 36/(37 − reps). It is often considered more accurate for lower rep ranges (2–5) and is widely used in collegiate strength programs.
Lombardi: Calculated as weight × reps^0.10. This formula produces slightly more conservative estimates and works well across a broad range of rep counts.

For the most accurate estimate, use a weight you can lift for 3–6 reps. Predictions become less reliable beyond 10 reps because muscular endurance begins to influence the result more than maximal strength.

Training with Percentages of Your 1RM

Once you know your estimated 1RM, you can program your training with precise intensity targets. Different percentage ranges produce different adaptations:

Strength (85–100%): Heavy loads with low reps (1–6) maximize neural drive and maximal force production. This range is the bread and butter of powerlifting programs and peaking phases.
Hypertrophy (67–85%): Moderate loads with moderate reps (6–12) optimize the mechanical tension and metabolic stress that drive muscle growth. Most bodybuilding and general fitness programs spend the majority of training time here.
Endurance (50–67%): Lighter loads with higher reps (15–30) build muscular endurance, improve work capacity, and can serve as effective deload or recovery work.

Progressive Overload and Retesting

Progressive overload — gradually increasing the demands placed on your muscles — is the fundamental driver of strength and muscle gains. You can achieve this by adding weight to the bar, performing more reps at the same weight, adding sets, or decreasing rest periods. As you get stronger, your 1RM will increase, so it is important to re-estimate every 4–8 weeks to keep your training percentages accurate and your progress on track.

Safety Tips for 1RM Testing

If you choose to test your actual 1RM rather than estimate it, follow these guidelines: warm up thoroughly with progressively heavier sets, always use a competent spotter or safety pins, maintain strict form throughout the lift, and avoid testing when fatigued or under-recovered. For most lifters, estimating from a 3–5 rep set is safer and nearly as accurate as a true max attempt.

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How to Use the One Rep Max (1RM) Calculator

1
Enter your values
Open the One Rep Max (1RM) Calculator and fill in the required input fields with your numbers or selections.
2
Review the calculation
The tool automatically computes the result as you type. Double-check your inputs to ensure accuracy.
3
Interpret your results
Review the calculated output along with any breakdowns, charts, or explanations provided to understand what the numbers mean for your situation.

Sources & Verification

Formulas based on peer-reviewed research cited by CDC and NIH

Centers for Disease Control and Prevention National Institutes of Health World Health Organization

Published by ConvertCrunch Editorial Team | Our Methodology

Frequently Asked Questions

What is the One Rep Max (1RM) Calculator?

The One Rep Max (1RM) Calculator is a free browser-based tool on ConvertCrunch. Estimate your 1RM via Epley, Brzycki, and Lombardi formulas. Percentage chart for training loads. It requires no downloads, installations, or account signups. Simply enter your values and get instant, accurate results. The tool is designed for quick calculations and informed decision-making, whether you are a professional, student, or everyday user looking for reliable answers.

How do I use the One Rep Max (1RM) Calculator?

Using the One Rep Max (1RM) Calculator is straightforward. Enter your values into the input fields provided on the page, then calculate or adjust parameters to explore scenarios. Most processing happens locally in your browser. If a feature uses a third-party service, the tool identifies that connection and the privacy policy explains it. Most users get the answers they need in under a minute.

Is the One Rep Max (1RM) Calculator free to use?

Yes, the One Rep Max (1RM) Calculator is completely free to use with no account signup, email requirement, or premium tier. Most calculations run locally in your browser. Features that depend on live data or a third-party service require a network connection and are identified in the tool. You can use it as many times as you need for personal, educational, or professional purposes.

How accurate is the One Rep Max (1RM) Calculator?

The One Rep Max (1RM) Calculator uses peer-reviewed scientific formulas that are widely accepted in clinical and fitness settings. Results are estimates based on population averages and may not perfectly reflect your individual physiology due to factors like genetics, body composition, and medical conditions. This tool is for informational purposes only and is not a substitute for professional medical advice. Consult a healthcare provider for personalized guidance.

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Understanding Your One-Rep Max (1RM)

How 1RM Formulas Work

Epley (1985): One of the most popular formulas, calculated as weight × (1 + reps/30). It tends to be slightly more accurate for higher rep ranges (6–10).
Brzycki (1993): Uses the formula weight × 36/(37 − reps). It is often considered more accurate for lower rep ranges (2–5) and is widely used in collegiate strength programs.
Lombardi: Calculated as weight × reps^0.10. This formula produces slightly more conservative estimates and works well across a broad range of rep counts.

Training with Percentages of Your 1RM

Once you know your estimated 1RM, you can program your training with precise intensity targets. Different percentage ranges produce different adaptations:

Strength (85–100%): Heavy loads with low reps (1–6) maximize neural drive and maximal force production. This range is the bread and butter of powerlifting programs and peaking phases.
Hypertrophy (67–85%): Moderate loads with moderate reps (6–12) optimize the mechanical tension and metabolic stress that drive muscle growth. Most bodybuilding and general fitness programs spend the majority of training time here.
Endurance (50–67%): Lighter loads with higher reps (15–30) build muscular endurance, improve work capacity, and can serve as effective deload or recovery work.