How accurate are 1RM calculators?

1RM calculators are generally accurate within 5-10% when used with rep ranges under 10. The accuracy depends on factors like training experience, muscle fiber composition, and the specific formula used. Our calculator uses 7 different formulas to give you the most comprehensive estimate.

Which 1RM formula is most accurate?

The Epley formula is most widely used and accurate for most people, especially with rep ranges of 2-10. However, different formulas work better for different individuals. Brzycki tends to be conservative, while Lombardi works well for powerlifters. Our calculator shows all 7 formulas so you can compare.

Can I use this for any exercise?

Yes, you can use 1RM calculators for any compound exercise like bench press, squat, deadlift, overhead press, and rows. The formulas are based on general strength principles that apply across exercises, though they're most accurate for compound movements.

What rep range should I use for the most accurate calculation?

For best accuracy, use rep ranges between 2-10 reps. The sweet spot is 3-8 reps where most formulas perform optimally. Avoid using very high rep ranges (15+) as the formulas become less reliable due to muscular endurance factors.

How often should I recalculate my 1RM?

Recalculate your 1RM every 4-6 weeks or whenever you notice significant strength gains. For beginners, monthly calculations work well. Advanced lifters might recalculate every 6-8 weeks. Always use recent max effort sets for the most accurate results.

Terms of Service

Last updated: January 2026

Important Safety Notice

This calculator provides estimates only. Always prioritize safety in your training. Consult qualified professionals before attempting maximum lifts.

1. Acceptance of Terms

By using the 1RM Calculator website and tools, you agree to be bound by these Terms of Service. If you do not agree to these terms, please do not use our service.

These terms apply to all users of the website, including casual visitors and regular users.

2. Description of Service

1RM Calculator is a free web-based tool that provides estimated one-repetition maximum calculations for strength training exercises using scientifically validated formulas.

Our service includes:

• One-rep max calculations using 7 different formulas
• Training percentage tables and recommendations
• Warm-up protocol suggestions
• Formula comparison and visualization tools
• Unit conversion between pounds and kilograms

3. Proper Use Guidelines

Permitted Uses:

• Personal strength training planning
• Educational and informational purposes
• Sharing results for training discussion
• Using as a reference tool for programming

Prohibited Uses:

• Copying or reproducing our calculation methods for commercial use
• Attempting to reverse engineer our algorithms
• Using automated tools to scrape or abuse the service
• Misrepresenting results or the source of calculations

4. Disclaimers and Limitations

Estimates Only

All calculations provided are estimates based on mathematical formulas. Actual performance may vary significantly based on individual factors including training experience, muscle fiber composition, fatigue, and technique.

No Medical Advice

This calculator is not a substitute for professional medical, fitness, or coaching advice. Consult qualified professionals before beginning any training program or attempting maximum lifts.

Safety Responsibility

Users are solely responsible for their safety during training. Always use proper form, appropriate spotters, and safety equipment when lifting heavy weights.

5. Limitation of Liability

To the fullest extent permitted by law, 1RM Calculator and its creators shall not be liable for:

• Any injuries or damages resulting from training based on our calculations
• Inaccurate estimates or calculation errors
• Service interruptions or technical issues
• Any indirect, incidental, or consequential damages

Your use of this service is at your own risk. We provide the tool "as is" without warranties of any kind.

6. Intellectual Property

The 1RM Calculator website, including its design, code, and unique implementation of calculation methods, is protected by intellectual property rights.

The underlying formulas (Epley, Brzycki, etc.) are public domain scientific formulas. However, our specific implementation, user interface, and presentation are our intellectual property.

You may not: Copy, reproduce, or create derivative works of our calculator for commercial purposes without permission.

7. Privacy

We respect your privacy and do not collect personal data. Your calculations are performed locally in your browser and are not stored on our servers.

For complete details, please review our Privacy Policy.

8. Service Availability

We strive to keep our service available 24/7, but we do not guarantee continuous availability. The service may be temporarily unavailable due to:

• Scheduled maintenance
• Technical issues or server problems
• Updates and improvements
• Circumstances beyond our control

9. Modifications to Terms

We may update these Terms of Service from time to time. Changes will be posted on this page with an updated revision date.

Continued use of the service after changes constitutes acceptance of the new terms.

10. Governing Law

These Terms of Service are governed by and construed in accordance with applicable laws. Any disputes shall be resolved through appropriate legal channels.

Questions About These Terms?

If you have any questions about these Terms of Service, please contact us:

legal@1rmcalculator.com