GainsLog
One Rep Max Calculator
Enter the weight you lifted and how many reps you completed. The calculator estimates your 1RM using five proven formulas and gives you a full training percentage table.
1–30 reps. Results are most accurate at 1–10 reps.
What is a one rep max?
Your one rep max (1RM) is the maximum weight you can lift for a single rep with good form. It's the standard metric for absolute strength — used in powerlifting competitions, strength testing protocols, and program design.
Most lifters don't test their true 1RM often because maximal singles are taxing and carry injury risk. Instead, they estimate it from a heavier submaximal set — usually 1–5 reps at a known load. This calculator does exactly that: take a recent work set and convert it to a reliable 1RM estimate.
How the formulas work
Several 1RM estimation formulas have been validated in research. Each uses a slightly different model to extrapolate from submaximal reps to a theoretical maximum:
- Epley: w × (1 + r/30). One of the most widely used, works well across a broad rep range.
- Brzycki: w × 36 / (37 − r). Very accurate at low rep counts (1–10), diverges above 15.
- Lander: (100 × w) / (101.3 − 2.67 × r). Validated against elite powerlifters.
This calculator averages Epley, Brzycki, Mayhew, Lombardi, and Lander to reduce the error from any single formula. For best accuracy, use a set of 1–5 reps performed close to failure.
How to use your 1RM
Your estimated 1RM becomes the anchor for all percentage-based programming. When a program says "work up to 85% for 3 sets of 3", you multiply your 1RM by 0.85 to get the working weight. This ensures load is scaled to your actual strength level rather than guessed.
Re-test or re-estimate your 1RM every 4–8 weeks (at the end of a training block) so your percentages stay accurate as you get stronger. GainsLog uses your logged weight, reps, and RIR to build adaptive targets automatically — no manual 1RM math required.
Reading the percentage table
The training percentage table shows the weight you should lift at each intensity zone. Heavy strength work typically falls at 85–95%; hypertrophy work at 65–80%; endurance-focused work below 65%. Most science-backed programs operate between 65–90% of 1RM to balance volume and recovery.
Frequently asked questions
How accurate is a 1RM calculator?
1RM estimates are most accurate when based on 1–5 rep sets performed close to failure. At higher rep ranges (10+) estimation error increases significantly — some research shows ±10–15% variability. For best results, use a challenging set of 3–5 reps as your input.
Should I test my actual 1RM in the gym?
For most recreational lifters, estimated 1RM from submaximal sets is safer and less fatiguing than true max testing. True 1RM tests make sense for powerlifters approaching competition. For general strength training, use this calculator and re-run it every mesocycle.
Why does the calculator average multiple formulas?
Each formula was derived from different study populations and has different accuracy at different rep ranges. Averaging reduces the impact of outliers and produces a more reliable estimate across the full 1–20 rep spectrum.
Learn the language
New to training terms like RPE, RIR, or mesocycle?
The GainsLog glossary defines every term you'll encounter in evidence-based training — from rep range concepts to periodization models.
Explore the glossary