How to Calculate Your One Rep Max (1RM)

Why Your One Rep Max Matters

Your one rep max is the benchmark that makes structured strength training possible. Without knowing your 1RM (or at least an estimate), you are guessing at how much weight to use for every set. That guesswork leads to either training too light (not enough stimulus for adaptation) or training too heavy (increased injury risk and poor recovery).

Percentage-based programs prescribe weights as a fraction of your 1RM. For example, the National Strength and Conditioning Association (NSCA) recommends training at 67 to 85 percent of 1RM for 6 to 12 repetitions to build muscle hypertrophy. The American College of Sports Medicine (ACSM) recommends 60 to 70 percent of 1RM for beginners and 80 to 100 percent for advanced lifters focused on maximal strength.

The Major 1RM Formulas Explained

Epley Formula

The Epley formula, developed by Boyd Epley in 1985, is the most commonly used 1RM estimation equation. It is the default formula in most fitness apps and online calculators.

1RM = Weight x (1 + Reps / 30)

Example: If you bench press 185 pounds for 6 reps, your estimated 1RM is 185 x (1 + 6/30) = 185 x 1.2 = 222 pounds.

Brzycki Formula

The Brzycki formula, published by Matt Brzycki in 1993, is the second most popular formula and produces nearly identical results to Epley for low rep counts.

1RM = Weight x (36 / (37 - Reps))

Using the same example: 185 x (36 / (37 - 6)) = 185 x (36 / 31) = 185 x 1.161 = 214.8 pounds. For 6 reps, the Brzycki formula gives a slightly lower estimate than Epley, which is typical for higher rep ranges.

Lombardi Formula

The Lombardi formula uses an exponential approach:

1RM = Weight x Reps^0.10

This formula is sometimes preferred for its simplicity and tends to give moderate estimates between the Epley and Brzycki results.

Which Formula Is Most Accurate?

Research comparing 1RM estimation formulas consistently shows that accuracy depends on the rep range used and the specific exercise. A validation study published by Southern Illinois University found that both the Epley and Brzycki formulas accurately predicted 1RM to within 2.7 and 3.1 kilograms, respectively, when using 5RM data for the back squat.

Key findings from the research literature:

• For 1 to 6 reps, the Epley and Brzycki formulas are equally accurate with errors of 2 to 3 percent.
• For 7 to 10 reps, the Epley formula tends to be more accurate, with errors of 3 to 5 percent.
• Above 10 reps, all formulas become unreliable, with errors of 5 to 10 percent or more.
• Formulas tend to underestimate 1RM for bicep curls, shoulder press, and leg extensions.
• Formulas tend to overestimate 1RM for tricep extensions and leg press.

The practical takeaway: use a weight you can lift for 3 to 5 reps with the Epley or Brzycki formula for the most reliable estimate.

How to Use Your 1RM for Training

Once you know your estimated 1RM, you can program training weights using percentages. Here is a standard percentage chart based on NSCA guidelines:

For example, if your estimated bench press 1RM is 225 pounds and you are training for hypertrophy, you would work with 157 to 191 pounds (70 to 85 percent of 225) for sets of 6 to 12 reps.

How to Estimate Your 1RM Safely

The safest way to estimate your 1RM is with a submaximal test. Here is the step-by-step process:

1. Warm up thoroughly. Perform 5 to 10 minutes of general cardio, then 2 to 3 warm-up sets of the target exercise with progressively heavier weights (e.g., 50 percent, 65 percent, and 80 percent of your expected working weight).
2. Select a challenging weight. Choose a weight you can lift for 3 to 5 reps with good form. You should reach near-failure on the last rep, meaning you could not complete another rep with proper technique.
3. Record the weight and reps. Be honest about rep count. Only count reps with full range of motion and controlled form.
4. Apply the formula. Use the Epley or Brzycki formula (or our 1RM calculator) to estimate your max.

Common Mistakes When Estimating 1RM

Using Too Many Reps

The more reps you use, the less accurate the estimate becomes. A set of 15 reps introduces fatigue variables that the formulas are not designed to account for. Stick to 10 reps or fewer for meaningful results, and ideally 3 to 5 reps.

Counting Partial Reps

If you do not complete the full range of motion, the rep does not count. A half-rep bench press where the bar only descends halfway uses significantly less muscle than a full rep, and including it inflates your estimated 1RM.

Testing When Fatigued

Your strength fluctuates based on sleep, nutrition, stress, and prior training. Estimate your 1RM when you are well-rested and adequately fueled. Testing after a heavy workout or a poor night of sleep can underestimate your true strength by 10 percent or more.

1RM Benchmarks: How Do You Compare?

Strength standards vary by body weight, sex, training experience, and exercise. Here are commonly cited benchmarks for the bench press based on data from ExRx.net and strength training literature, expressed as multiples of body weight:

The Bottom Line

Your one rep max is the foundation of intelligent strength training. Rather than testing it directly (which carries injury risk), estimate it using the Epley or Brzycki formula with a 3 to 5 rep set. The result is accurate within 2 to 5 percent for trained lifters and gives you the numbers you need to program effective workouts at the right intensity.

Estimate your 1RM with our free one rep max calculator, which runs your numbers through multiple formulas simultaneously.

Frequently Asked Questions