One-Rep Max Calculator

A one-rep max (1RM) calculator estimates the maximum weight you can lift for one repetition based on a weight you can lift for multiple reps. Essential for strength training program design, tracking progress, and determining training weights for different rep ranges.

What is One-Rep Max?

One-rep max is the heaviest weight you can successfully lift for one complete repetition with proper form. It's the gold standard for measuring absolute strength and is used to:

Design training programs (percentages of 1RM)
Track strength progress over time
Compare strength across different exercises
Set realistic training goals

1RM Formulas

Brzycki Formula (Most Common)

1RM = Weight / (1.0278 - 0.0278 × Reps)

Most widely used, generally accurate for 2-6 rep ranges. Developed by Matt Brzycki.

Epley Formula

1RM = Weight × (1 + Reps / 30)

Simple and popular. Works well for moderate rep ranges (3-10 reps).

Lombardi Formula

1RM = Weight × Reps^0.1

Good for powerlifting movements. Uses exponential calculation.

Mayhew Formula

1RM = (100 × Weight) / (52.2 + 41.9 × e^(-0.055 × Reps))

More complex, accounts for fatigue curves. Good for higher rep ranges.

O'Conner Formula

1RM = Weight × (1 + 0.025 × Reps)

Simple linear formula. Less accurate but easy to calculate mentally.

Accuracy Considerations

Most Accurate Rep Ranges

2-6 reps: Most accurate for 1RM estimation
1 rep: Already your 1RM (no calculation needed)
3-5 reps: Sweet spot for accurate estimation

Less Accurate Rep Ranges

10+ reps: Formulas become less reliable
15+ reps: Very inaccurate, don't use for 1RM estimation
Failure sets: If form broke down, calculation will be off

Training Percentages

Once you know your 1RM, you can calculate training weights:

100% (1RM): Maximum strength - 1 rep
90-95%: Very heavy - 2-3 reps
85-90%: Heavy - 3-5 reps
80-85%: Moderate-heavy - 5-6 reps
70-80%: Moderate - 6-10 reps
60-70%: Light-moderate - 10-15 reps
50-60%: Light - 15-20 reps

When to Test Actual 1RM

Good Times to Test

After 4-8 weeks of training
When you feel strong and recovered
With proper warm-up and spotter
For competition preparation

Don't Test 1RM When

You're a beginner (use calculators instead)
You're injured or recovering
You're fatigued or overtrained
You don't have a spotter (for safety)

Safety Considerations

Always warm up: Progressively increase weight before max attempts
Use a spotter: Essential for bench press and overhead movements
Proper form: Don't sacrifice form for weight
Know your limits: Don't attempt 1RM if you're unsure
Use safety equipment: Power rack, safety bars, collars
Listen to your body: Stop if something feels wrong

Using 1RM for Program Design

Strength Programs

Focus on 85-95% of 1RM for 1-5 reps. Builds maximum strength.

Hypertrophy Programs

Focus on 70-85% of 1RM for 6-12 reps. Builds muscle size.

Endurance Programs

Focus on 50-70% of 1RM for 12-20+ reps. Builds muscular endurance.

Common Exercises

1RM is commonly tested for:

Bench Press: Upper body pushing strength
Squat: Lower body strength
Deadlift: Posterior chain strength
Overhead Press: Shoulder strength
Barbell Row: Back strength

Factors Affecting 1RM

Training experience: More experience = higher 1RM
Muscle mass: More muscle = more strength potential
Technique: Better form = more efficient = higher 1RM
Recovery: Well-rested = stronger
Nutrition: Adequate calories and protein support strength
Age: Strength peaks in 20s-30s, declines gradually
Genetics: Muscle fiber type and leverage affect strength

Progressive Overload

To increase your 1RM over time:

Train consistently: Regular strength training sessions
Progressive overload: Gradually increase weight, reps, or volume
Recovery: Adequate sleep and nutrition
Periodization: Vary intensity and volume over time
Patience: Strength gains take time - weeks to months

1RM vs Training Max

Some programs use a "training max" (90-95% of true 1RM) to:

Reduce injury risk
Allow for consistent progress
Account for daily fluctuations
Make calculations easier

Example: If your true 1RM is 300 lbs, your training max might be 285 lbs (95%).

Strength Training Tip: While 1RM is useful for program design, you don't need to test it frequently. Use calculators based on your training sets, and only test actual 1RM when you're experienced, properly warmed up, and have a spotter. Focus on consistent training and progressive overload - your calculated 1RM will increase over time!

One-Rep Max Calculator