Why this matters
Every strength training program worth following is built around percentages of your one-rep max. Whether you are running a linear periodization block, a 5/3/1 variant, or a conjugate split, you need a reliable 1RM figure to load your working sets correctly. Guessing leads to under-training or, worse, unnecessary injury risk from loading too aggressively.
Testing a true single-rep max requires maximal effort under heavy load, which carries real risk for anyone who is not a competitive powerlifter. Submaximal estimation lets you work backward from a set of 3, 5, or even 10 reps and arrive at a projected max without ever grinding a one-rep attempt. The seven formulas supported here each model the strength-reps curve slightly differently, giving you a range rather than a single blind number.
The seven estimation formulas
| Formula | Best rep range | Key characteristic |
|---|---|---|
| Epley | 5–10 reps | Most widely used in commercial gyms |
| Brzycki | ≤5 reps | Tends to be most accurate at low reps |
| Lander | 3–8 reps | Conservative estimates |
| Lombardi | 1–5 reps | Exponential model, aggressive at high reps |
| Mayhew | 1–10 reps | Polynomial model, popular in research |
| O’Conner | 2–8 reps | Similar to Epley with slight adjustments |
| Wathen | 2–8 reps | Research-backed, good all-rounder |
How to use it
Enter the weight you lifted in kilograms.
Enter the number of reps you performed (the tool accepts 1 through 15).
Select a single formula or compare estimates across all seven at once.
Review your projected 1RM and the automatic training-percentage breakdown.
Testing your result
To verify your estimated 1RM, warm up progressively and attempt a single rep at 95% of the projected number. If you complete it with good form, the estimate is reasonably accurate. If you fail or your form breaks down significantly, your true max likely sits a bit lower than predicted. Retest every 4–8 weeks using the same formula so your comparisons stay consistent and your program adjustments are data-driven rather than guesswork.
Common mistakes
Using a rep count above 10, where all formulas lose accuracy because the strength-reps relationship becomes nonlinear.
Comparing results from different formulas week to week instead of sticking to one for consistent tracking.
Forgetting that estimation formulas assume you reached muscular failure on that set — stopping two reps short invalidates the math.
Using the 1RM of a compound lift to program isolation exercises, which have a different rep-strength curve.
Edge cases and options
If you enter exactly 1 rep, every formula returns the weight you entered since no estimation is needed. Rep counts above 10 produce increasingly unreliable numbers because fatigue, not just maximal strength, limits performance at those ranges. The training-percentage table shows what weight to load for common rep targets (3, 5, 8, 10, 12 reps), which is the output most lifters actually need from a 1RM calculator day to day.
Real-world use cases
A powerlifter estimates their squat 1RM from a triple at 140 kg to set upcoming peaking block intensities.
A personal trainer uses the training-percentage breakdown to write a progressive overload program for a novice client.
A CrossFit athlete compares Brzycki vs. Epley on their clean and jerk to sanity-check whether their numbers are realistic for competition.
A rehabilitation specialist tracks submaximal strength gains in a returning athlete without exposing them to maximal loads.
Frequently asked questions
Q: Which formula is best?
A: Epley and Brzycki are the most popular. Brzycki tends to be more accurate at low reps (≤5), Epley at moderate reps (5–10). All formulas lose accuracy above 10 reps.
Q: Why use percentages of 1RM?
A: Strength training programs are typically expressed as a percentage of 1RM. 80% of 1RM corresponds to roughly 8 reps, 90% to about 4 reps, and 95% to approximately 2 reps. These percentages let you program specific training stimuli without guessing.
Q: Should I test my true 1RM?
A: Only experienced lifters should attempt true 1RM testing. Always use a spotter, warm up thoroughly, and stop if form breaks down. Submaximal estimation is safer for most people.
Q: How often should I retest?
A: Every 4–8 weeks is typical. Use the same formula each time so comparisons are consistent.
Q: Can I compare 1RMs across different lifts?
A: You can compare relative strength by dividing your 1RM by body weight. Raw 1RMs across lifts (squat vs. bench) are not directly comparable because muscle groups differ in absolute strength potential.
Start using it now
Try the 1RM Calculator tool. See also Workout Plan Generator and Exercise Calorie Burn for complementary fitness planning.
