What Is a Rep Max Calculator?
A rep max calculator answers a common training question: if you know
your weight for one rep count, what weight should you use for a
different rep count? This is how to calculate your 1RM without maxing
out, then work in the opposite direction — from your estimated 1RM to
any target rep range, whether that's a heavier 3-rep set or a lighter
15-rep set.
It works in two steps: first, your known weight and reps are converted
into an estimated one rep max (1RM) using an established formula.
Then, that 1RM is converted back down to the weight matching your
target rep count using the same formula's curve.
How to Use This Calculator
Enter a weight and rep count you've already performed for a clean
set, then enter the rep count you want to train at. Choose a formula
and unit, then calculate. The result table also shows estimated
weights across a full range of rep counts, so you can plan multiple
training days from a single data point.
Percentage-Based Training: What Percentage Should You Use?
Rep max and 1RM percentages are the foundation of percentage-based
training programs. Once you know your estimated max, the rep range
you train in determines what adaptation you're driving:
- 80%–100% (1–5 reps): Strength and power. Recruits maximum motor units but carries the highest CNS fatigue cost — this is the most taxing zone on your central nervous system, so keep sessions in this range infrequent.
- 70%–85% (6–12 reps): Hypertrophy. The most efficient zone for 1RM percentages for muscle growth, balancing mechanical tension with manageable fatigue.
- 50%–70% (12–20+ reps): Muscular endurance. Lower CNS demand per set, useful for conditioning, deloads, or high-volume accessory work.
Epley vs. Brzycki vs. Lander vs. Lombardi
There is no single best formula for every lifter — comparing a few
gives a more reliable picture. Here's how each one handles the
rep-to-weight conversion:
1. Epley Formula
1RM = Weight × (1 + Reps / 30)
One of the most widely validated equations in strength training
literature. Best for: converting between rep ranges
of 1–10.
2. Brzycki Formula
1RM = Weight × 36 / (37 − Reps)
Slightly more conservative than Epley, especially at higher reps.
Best for: cross-checking Epley results in the 1–8
rep range.
3. Lander Formula
1RM = (100 × Weight) / (101.3 − 2.67123 × Reps)
A stable linear model. Best for: moderate rep
conversions (6–12 reps).
4. Lombardi Formula
1RM = Weight × Reps^0.10
A non-linear model that scales gently for higher reps.
Best for: converting to or from high target rep
counts (12+ reps).
Frequently Asked Questions
How accurate is a 1RM calculator?
Typically accurate within 5-10% for sets of 1-10 reps. Beyond 10 reps, fatigue makes the estimate less reliable.
Which 1RM formula is the best to use?
There's no single best formula — comparing Epley, Brzycki, Lander, and Lombardi gives a more complete picture, especially at higher rep ranges.
Should I test a true 1RM or use an estimator?
Estimating is safer for most lifters — testing a true max places high stress on your CNS and connective tissues.
What percentages of my 1RM should I use for different goals?
80-100% for strength (1-5 reps), 70-85% for hypertrophy (6-12 reps), 50-70% for endurance (12-20+ reps).
Does this work the same for men and women?
Yes, these are general-population formulas used for both men and women, though minor accuracy differences can appear at higher rep ranges.