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One Rep Max (1RM) Calculator with Training Percentages

Estimate your one-rep max for bench press, squat, deadlift and more from a set of 1–12 reps, plus a percentage table for strength and muscle training.

Estimate your 1RM

Switch units with the lb/ft – kg/cm toggle at the top of the page. Nothing you enter leaves your device.

What is a one-rep max?

Your one-rep max (1RM) is the heaviest weight you can lift for one complete repetition with good form. Testing it directly is risky without experience, a spotter and safety equipment. A safer way is to estimate it from a set of several reps.

Formulas we use

  • Epley: 1RM = weight × (1 + reps ÷ 30)
  • Brzycki: 1RM = weight × 36 ÷ (37 − reps)

We show the average of both. Estimates are most accurate for sets of 2–10 reps.

How to use your 1RM

Programs often prescribe weights as a percentage of 1RM. Roughly: 85–100% builds maximal strength (1–5 reps), 65–85% is ideal for muscle growth (6–12 reps), and below 65% builds muscular endurance (15+ reps). Muscle can grow across a wide range of loads as long as sets are taken close to failure.

Safety tips for heavy lifting

  • Always warm up with progressively heavier sets.
  • Use safety pins or a spotter for bench press and squats.
  • Stop a set when your form breaks down.
  • Beginners should focus on technique for several months before testing heavy singles.

How to use your result

A calculator gives you a starting point, not a final answer. The most reliable way to use any fitness number is the measure → act → review loop:

  1. Measure: record your result today, along with your morning body weight, waist measurement and a few photos.
  2. Act: follow a matching plan for 2–4 weeks. Use the plan builder to get a workout program and a 7-day meal plan that fit your numbers.
  3. Review: compare your weekly averages and measurements. If things are moving in the right direction at a sustainable pace, keep going. If not, adjust by small amounts (100–200 calories, one extra workout, 2,000 extra steps) and review again.

US and metric units

Every HelloMyTrainer calculator works in both systems. Use the lb / ft or kg / cm switch at the top of the page; your choice is remembered on this device for all calculators and meal plans. Useful conversions: 1 kg = 2.2 lb, 1 inch = 2.54 cm, 1 foot = 30.48 cm, 1 liter = 33.8 US fluid ounces.

Who should be careful with these numbers

These calculators are designed for healthy adults aged 18 and over. They are not suitable for children or teenagers, pregnant or breastfeeding women, people with a history of eating disorders, competitive athletes with very high muscle mass, or people with medical conditions that affect weight, metabolism or fluid balance (such as heart failure, kidney disease or thyroid disorders). If any of these apply to you, please speak with your doctor or a registered dietitian before using the results.

Your privacy

We never ask for your name, email or any personal details to use our tools. The calculations run in your web browser and the numbers you type are not sent to our servers. See our Privacy Policy for details.

Frequently asked questions

Is it safe to test my 1RM?

For experienced lifters with good technique and safety equipment, yes. Beginners should use this estimate instead.

Which exercises can I use this for?

Compound lifts such as bench press, squat, deadlift, overhead press and rows. It is less accurate for isolation exercises.

How often should I retest?

Every 6–12 weeks, or use your training sets to re-estimate regularly.

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Results are estimates for healthy adults and are not medical advice.