Brzycki Formula: How to Calculate Your 1RM
Learn the Brzycki formula for estimating your one-rep max. Understand when to use it, its accuracy, and how it compares to Epley.
What is the Brzycki formula for 1RM?
The Brzycki formula estimates your 1RM as: 1RM = weight x 36/(37 - reps). It's considered more conservative than Epley for higher rep ranges (6+), making it popular among strength coaches. For example, if you squat 100kg for 5 reps, your estimated 1RM is 112.5kg.
TL;DR
- •Brzycki formula: 1RM = weight x 36 / (37 - reps). Conservative and widely trusted for low rep ranges.
- •Most accurate for 1-6 reps. Accuracy drops above 10 reps and is undefined at 37 reps.
- •More conservative than Epley, making it safer for programming training loads and competition prep.
- •Developed by Matt Brzycki in 1993 at Princeton University. One of the most cited 1RM equations.
What Is the Brzycki Formula?
The Brzycki formula is one of the most widely used equations for estimating your one-rep max (1RM) from submaximal lifts. Published by Matt Brzycki in 1993, it provides a mathematical way to predict the maximum weight you could lift for a single repetition based on the weight and reps you performed.
The formula uses an inverse relationship where as reps approach 37, the denominator approaches zero and the estimated 1RM approaches infinity. This means the formula has a built-in theoretical maximum of 36 reps, which aligns well with observed limits on muscular endurance for most compound lifts.
How the Brzycki Formula Works
Let's walk through a step-by-step calculation:
You bench press 80kg for 6 reps
- Identify your values: weight = 80kg, reps = 6
- Plug into the formula: 1RM = 80 x 36 / (37 - 6)
- Calculate the denominator: 37 - 6 = 31
- Calculate the numerator: 80 x 36 = 2,880
- Divide: 2,880 / 31 = 92.9kg
Your estimated 1RM is 92.9kg
Compare this to Epley's estimate for the same set: 80 x (1 + 6/30) = 96.0kg. Brzycki gives a more conservative estimate by 3.1kg.
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Use our free calculator to estimate your one rep max using the Brzycki formula and compare with other formulas.
Use Free ToolWhen to Use the Brzycki Formula
- Low rep training (1-6 reps): Brzycki is most accurate in this range, closely matching actual 1RM test results in research studies.
- Competition preparation: The conservative estimates help you plan attempt selections without overreaching. Better to underestimate than fail an attempt.
- Percentage-based programs: When your program prescribes weights as percentages of 1RM, Brzycki keeps training loads manageable.
- Tracking strength progress: Consistently using one formula lets you compare estimated 1RM over time, even if the absolute number differs from your true max.
Accuracy and Limitations
Understanding when the Brzycki formula is reliable and when it falls short:
Brzycki excels here. Estimates are typically within 2-5% of tested 1RM values. This is the formula's sweet spot.
Still reliable, but Epley may match or slightly outperform Brzycki in this range. The difference between the two formulas is usually 2-4%.
Brzycki tends to underestimate compared to actual test results. Individual variation in muscular endurance becomes a significant factor.
Accuracy is poor. The formula approaches its mathematical limit (37 reps). Use a heavier weight with fewer reps instead.
- Trained lifters may find Brzycki slightly underestimates their true 1RM, especially on competition lifts with adrenaline.
- The formula was validated primarily on compound barbell movements (squat, bench, deadlift). It may be less accurate for isolation exercises or machines.
- Individual differences in muscle fiber composition affect accuracy. Fast-twitch dominant lifters may exceed Brzycki estimates.
Brzycki vs Epley
Here's how Brzycki and Epley compare when estimating 1RM from different rep counts, using 100kg as the working weight:
| Reps @ 100kg | Brzycki | Epley | Difference |
|---|---|---|---|
| 1 rep | 100kg | 100kg | 0kg |
| 3 reps | 105.9kg | 110kg | +4.1kg |
| 5 reps | 112.5kg | 116.7kg | +4.2kg |
| 8 reps | 124.1kg | 126.7kg | +2.6kg |
| 10 reps | 133.3kg | 133.3kg | 0kg |
| 12 reps | 144kg | 140kg | -4kg |
- At 1 rep, both formulas return the actual weight (no estimation needed).
- The gap widens with more reps. Brzycki is always equal or lower than Epley.
- For 5 reps, the difference is 4.2kg. For 10 reps, it grows to 7.4kg.
Practical Applications
- Program design: If your program says "5x5 at 75%", use Brzycki to estimate your 1RM, then calculate 75% of that. The conservative estimate means you won't overshoot.
- Auto-regulation: Track your Brzycki-estimated 1RM weekly. If it trends up over weeks, you're getting stronger. If it plateaus, consider adjusting your program.
- Meet prep: Use your best Brzycki estimates from training to plan opener, second, and third attempts. Add 2-5% for competition adrenaline effect.
- Testing protocol: For the most accurate Brzycki estimate, perform a set of 3-5 reps after full warm-up with 3-5 minutes rest. Use strict form throughout.
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Try it freeFrequently Asked Questions
What is the Brzycki formula?
The Brzycki formula is a mathematical equation for estimating your one-rep max (1RM): 1RM = weight x 36 / (37 - reps). It was developed by Matt Brzycki in 1993 and is widely used in strength training for programming percentages and tracking progress without maximal testing.
How accurate is the Brzycki formula?
The Brzycki formula is most accurate in the 1-6 rep range, typically within 5% of your true 1RM. Accuracy decreases above 10 reps due to individual differences in muscular endurance. It tends to be more conservative than Epley, making it a safer choice for programming training loads.
When should I use Brzycki vs Epley?
Use Brzycki when working with low rep ranges (1-6 reps), when you prefer conservative estimates, or for competition preparation. Use Epley for mid-range rep sets (6-10 reps) or when you want slightly more aggressive estimates. Both are valid; consistency matters more than formula choice.
Does the Brzycki formula work for high rep ranges?
The Brzycki formula becomes increasingly unreliable above 10 reps and is mathematically undefined at 37 reps (division by zero). For sets above 10 reps, consider using the Epley formula or, better yet, test with a heavier weight in the 3-6 rep range for a more accurate estimate.
Who is Matt Brzycki?
Matt Brzycki is a strength and conditioning professional who published the formula in 1993 while working at Princeton University. He authored several books on strength training and is known for his evidence-based approach to exercise science. His formula remains one of the most cited 1RM prediction equations.