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 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 commonly used in percentage-based
training programs. Once you know your estimated max, the rep range
you train in can help guide loading, although the appropriate
percentage varies by exercise, goal, training experience, and
individual response:
- 80%–100% (1–5 reps): Often used for strength and power work. Heavier loads generally place more demand on technique and fatigue management, so appropriate exercise selection, preparation, and recovery matter.
- 70%–85% (6–12 reps): Commonly used for hypertrophy-oriented training, providing substantial mechanical tension while allowing more repetitions than very heavy loading.
- 50%–70% (12–20+ reps): Often used for lighter, higher-rep work and muscular endurance, and can be useful for accessory exercises or higher-volume training depending on the program.
Epley vs. Brzycki vs. Lander vs. Lombardi
There is no single best formula for every lifter — comparing a few
gives a broader picture. Here's how each one handles the
rep-to-weight conversion:
1. Epley Formula
1RM = Weight × (1 + Reps / 30)
One of the most commonly used equations for estimating 1RM from
submaximal performance. Best for: general
rep-to-weight conversions, particularly at lower to moderate rep
counts.
2. Brzycki Formula
1RM = Weight × 36 / (37 − Reps)
A commonly used linear-style 1RM equation. Its estimate can differ
from Epley depending on the rep count, and it's mathematically
defined only up to 36 reps. Best for: comparing
estimates at lower to moderate rep counts.
3. Lander Formula
1RM = (100 × Weight) / (101.3 − 2.67123 × Reps)
A linear equation that produces a different estimate from Epley and
Brzycki as rep counts increase, and is mathematically defined up to
37 reps. Best for: comparing moderate-rep estimates,
keeping in mind that higher-rep predictions are more sensitive to
the formula used.
4. Lombardi Formula
1RM = Weight × Reps^0.10
A non-linear model using a power relationship between reps and
estimated 1RM, with no upper rep limit. Best for:
comparing estimates across a wider range of rep counts, including
higher-rep inputs.
Frequently Asked Questions
How accurate is a 1RM calculator?
1RM calculators provide estimates rather than exact measurements. Lower to moderate rep sets tend to give more consistent estimates, while higher-rep sets can be less reliable because fatigue and individual differences have a larger effect.
Which 1RM formula is the best to use?
There's no single best formula — comparing Epley, Brzycki, Lander, and Lombardi can give a broader picture, especially when results differ at higher rep ranges.
Should I test a true 1RM or use an estimator?
Estimating from a submaximal set is a practical alternative for many lifters. A true max attempt benefits from appropriate technique, preparation, and safety precautions, especially for heavy compound lifts.
What percentages of my 1RM should I use for different goals?
Common starting ranges include 80-100% for lower-rep strength work (1-5 reps), 70-85% for many hypertrophy-oriented sets (6-12 reps), and 50-70% for lighter, higher-rep endurance work (12-20+ reps). Individual programming may vary.
Does this work the same for men and women?
Yes, these general-population formulas can be used for both men and women. Individual accuracy can vary based on the exercise, training experience, rep range, and individual performance.