1RM Formulas Compared: Which Is Most Accurate?

Why Estimate Your 1RM?

Your one-rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It's useful for:

• Programming: Many programs prescribe weights as percentages of 1RM (e.g., "5 sets of 5 at 75%")
• Tracking progress: Compare estimated 1RM over time without the injury risk of frequent maximal attempts
• Determining strength level: Use with strength standards to know where you stand
• Competition prep: Plan attempt selections for powerlifting meets

Rather than testing your true 1RM (which carries injury risk), you can estimate it from submaximal lifts using mathematical formulas.

The Three Main Formulas

Epley Formula

Developed by Boyd Epley in the 1980s, this is perhaps the most widely used formula. It assumes a linear relationship between reps and percentage of max.

• Origin: National Strength and Conditioning Association (NSCA)
• Best for: Mid-range rep sets (6-10 reps)
• Pros: Simple to calculate mentally, widely validated
• Cons: May overestimate at very high reps

Example: 100kg × 5 reps → 100 × (1 + 5/30) = 100 × 1.167 = 116.7kg

Brzycki Formula

Created by Matt Brzycki in 1993, this formula uses an exponential curve that becomes increasingly steep as reps approach the theoretical maximum of 37.

• Origin: Princeton University research
• Best for: Lower rep ranges (1-6 reps)
• Pros: More conservative estimates, good for heavy training
• Cons: Undefined at 37+ reps, can underestimate for some lifters

Example: 100kg × 5 reps → 100 × (36 / (37 - 5)) = 100 × 1.125 = 112.5kg

Lander Formula

Jim Lander's formula provides estimates that typically fall between Epley and Brzycki. It uses a different linear regression approach.

• Origin: Regression analysis of powerlifting data
• Best for: General use across rep ranges
• Pros: Balanced estimates, good middle ground
• Cons: Less widely known, undefined at ~38 reps

Example: 100kg × 5 reps → (100 × 100) / (101.3 - 13.36) = 10000 / 87.94 = 113.7kg

Formula Comparison

Here's how the three formulas compare when calculating 1RM from different rep counts, using 100kg as the working weight:

Notice how the formulas converge at low reps (where estimation is most accurate) and diverge significantly at higher reps (where accuracy decreases).

Accuracy at Different Rep Ranges

Which Formula Should You Use?

For most practical purposes, the differences between formulas are small enough that any choice works. Here's our recommendation:

• For consistency: Pick one formula and stick with it. Progress tracking matters more than absolute accuracy.
• For accuracy: Use the average of all three formulas. Our 1RM calculator does this automatically.
• For programming: Epley is most commonly referenced in training literature and percentage charts.
• For competition: Use Brzycki for more conservative estimates when planning meet attempts.

When 1RM Formulas Are Less Accurate

Several factors can cause formulas to over- or underestimate your true max:

• Exercise selection: Formulas were developed primarily for squat, bench, and deadlift. They may be less accurate for Olympic lifts or isolation exercises.
• Training background: Endurance athletes may have better rep-out performance relative to their max. Powerlifters the opposite.
• Muscle fiber composition: Fast-twitch dominant individuals perform better at low reps relative to their high-rep performance.
• Technique breakdown: If form degrades significantly as reps increase, the set may end due to technique limits rather than strength limits.
• Mental factors: True 1RM attempts require significant psychological arousal that can't be replicated in formula-based estimation.

Practical Tips for Accurate Estimation

1. Use 3-6 reps for best accuracy. This range balances the signal (strength) to noise (fatigue, technique) ratio optimally.
2. Rest fully before your estimation set. 3-5 minutes ensures you're not limited by recovery from previous sets.
3. Use strict form throughout. Sloppy reps inflate rep counts artificially.
4. Note your RPE/RIR. A set of 5 at RPE 10 estimates differently than 5 reps with 2 left in the tank.
5. Average multiple data points. Your estimated 1RM from 100kg x 5 and from 90kg x 8 should be similar. If they diverge significantly, investigate why.