Matt Brzycki published his 1RM estimation formula in a 1993 Strength & Conditioning journal article. Three decades later it's still one of the two most-used formulas in strength training — the other being Epley. If you've ever pulled a 1RM estimate from a spreadsheet or a calculator app, there's a good chance Brzycki was the equation running under the hood. This is the full breakdown: how it works, where it wins, where it fails, and how to actually apply it to your programming.

The Formula

Brzycki's equation is deceptively simple:

1RM = weight × 36 / (37 − reps)

Plug in the weight lifted and the number of reps completed. The denominator does the heavy lifting — as reps go up, (37 − reps) shrinks, pushing the estimated 1RM higher relative to the working weight.

A worked example: you bench 100 kg for 5 reps.

1RM = 100 × 36 / (37 − 5) = 3600 / 32 = 112.5 kg

So a 5-rep max at 100 kg predicts a true 1RM around 112.5 kg. Compare that to Epley's estimate from the same set (116.7 kg) — a 4 kg gap that shows why formula choice matters.

Where the Formula Comes From

Brzycki analyzed data from Nebraska football players in the late 1980s and early 90s. He was looking for a simple bench-press prediction tool a coach could apply in the field without a calculator. The 36/37 ratio wasn't derived from first principles — he fit it empirically to the data he had. It happened to fit well enough that it stuck.

The key detail: the original dataset was college-aged men doing bench press in the 1-10 rep range. Every accuracy claim about Brzycki traces back to that population. Push the formula outside those bounds — 15+ rep sets, older lifters, exercises with different mechanical profiles — and the fit degrades.

Rep-Load Percentage Table

The Brzycki formula produces a clean set of load percentages that lifters have memorized for decades:

  • 1 rep: 100% of 1RM
  • 2 reps: 97.2% of 1RM
  • 3 reps: 94.4% of 1RM
  • 4 reps: 91.7% of 1RM
  • 5 reps: 88.9% of 1RM
  • 6 reps: 86.1% of 1RM
  • 7 reps: 83.3% of 1RM
  • 8 reps: 80.6% of 1RM
  • 9 reps: 77.8% of 1RM
  • 10 reps: 75.0% of 1RM

These are the numbers behind most percentage-based programs. A "3x5 at 85%" prescription is essentially asking you to work at your Brzycki 5RM predicted load.

Where Brzycki Beats Epley

Head-to-head research (LeSuer et al. 1997, Wood et al. 2002) compared Brzycki and Epley against real 1RM tests. Brzycki was more accurate in the 5-10 rep range, particularly on bench press. The reason has to do with how the two formulas behave as reps climb:

  • Epley adds a fixed fraction (reps/30) to the weight — a linear scaling that starts overpredicting past 6-7 reps.
  • Brzycki uses an inverse relationship (36 / (37 − reps)) that grows more slowly and more accurately reflects how humans actually fatigue.

Practical translation: for a lifter running a 5x5 or 3x8 hypertrophy block, Brzycki gives more usable 1RM estimates. For a powerlifter working in the 1-3 rep range, Epley is often preferred.

Where Brzycki Breaks Down

  • Above 12 reps. The formula becomes mathematically unstable. At 15 reps, (37 − 15) = 22, and small variations in rep count produce wild swings in the estimate. Never apply Brzycki to sets of 13+.
  • Deadlifts and cleans. High-neural-drive lifts follow different fatigue curves than bench press. Brzycki underpredicts deadlift 1RM by 3-6% in some studies.
  • Untrained lifters. Coordination and technique errors on submaximal sets produce misleading rep counts. Formulas work best with 6+ months of consistent training experience.
  • To-failure vs stopped-with-reps-in-reserve sets. Brzycki assumes the reported rep count is true failure. Stopping 1-2 reps short of failure inflates the estimate significantly.

How to Use the Brzycki Formula in Practice

Three common applications:

1. Setting training percentages

Take your working set weight and rep count, plug into Brzycki, and use the estimated 1RM as your reference for percentage-based programming. Update the reference every 3-4 weeks — don't drag last month's number into this month's block.

2. Cross-checking Epley

Run both Epley and Brzycki on the same set. If they agree within 3-4 kg, the estimate is probably reliable. If they diverge by more than 6-7 kg (usually at higher rep counts), lean toward the lower number for safety.

3. Programming safety margin

When prescribing heavy singles (90%+) from an estimated 1RM, always use the more conservative formula. For most rep ranges that's Brzycki — going with the lower estimate reduces failed rep and injury risk.

Common Programming Mistakes

  • Using a max-effort 5RM in a formula, then programming based on the result the same week. The lift you use to generate the estimate was already taxing. Give the CNS 5-7 days of lower intensity before running heavy percentages off it.
  • Recycling old 1RM estimates for months. Brzycki-estimated 1RMs drift up and down as training age, sleep, and stress change. Recalculate every 3-4 weeks.
  • Applying Brzycki to sets where you left reps in reserve. If you stopped a set at 8 reps but could have hit 10, the formula thinks 8 was your absolute max — and the resulting 1RM estimate will be 6-8% too low.
  • Cross-lift generalization. A Brzycki estimate from your squat doesn't tell you anything useful about your bench press 1RM. Estimate each lift separately.

Brzycki vs Real 1RM Testing

The LeSuer 1997 study measured actual 1RM against Brzycki-predicted 1RM in college-aged athletes. Results:

  • Bench press: Brzycki over-estimated actual 1RM by an average of 1.2%.
  • Squat: Brzycki under-estimated by an average of 4.2%.
  • Deadlift: Brzycki under-estimated by an average of 3.8%.

Translation: the formula is most reliable for bench and least reliable for pulls. When Brzycki tells you your deadlift 1RM is 200 kg, the real number is probably closer to 208 kg.

Adjustments for Different Populations

  • Advanced lifters (5+ years): Brzycki tends to underpredict by 2-4% at high rep counts because neural efficiency lets experienced athletes push closer to true failure. Bump the estimate up slightly for programming.
  • Older lifters (40+): Fatigue accumulates faster past 40. Brzycki predictions from 8+ rep sets often overestimate by 3-5%. Use lower rep sets as your reference.
  • Female lifters: Available research (limited) suggests Brzycki performs slightly better for women than Epley, but the sample sizes are small. Track your own predicted-vs-real ratio over time.

Using Brzycki with Our Calculator

Plug your weight and rep count into the 1RM Calculator — it runs both Brzycki and Epley automatically and shows you both estimates side by side. When they agree, trust the average. When they diverge, use the lower number if you're about to attempt a heavy percentage, and the higher number if you're setting a stretch goal.

Related Cluster Reading

Bottom Line

The Brzycki formula is a reliable 1RM estimator in the 3-10 rep range, most accurate on bench press, slightly conservative on squats and deadlifts. It beats Epley in the 5-10 rep range where most hypertrophy work happens. Don't use it above 12 reps, don't apply it across lifts, and don't rely on estimates older than 3-4 weeks. For programming safety, average Brzycki and Epley — the result is the working number that most coaches use in practice.