One Rep Max Calculator
Estimate your one repetition maximum from a set you have already completed, using three standard formulas.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
Epley, Brzycki and Lombardi are estimates from the entered load and repetition count. Their arithmetic mean is a comparison value, not a measured maximum or proof of improved accuracy. Exercise, technique, fatigue and repetition range affect agreement; do not treat the estimate as a safe load to attempt.
Worked example
calculated with the default values below
Weight lifted 100 kg · Repetitions completed 5 reps Epley 116.7 kg · Brzycki 112.5 kg · Lombardi 117.5 kg · Average estimate 115.5 kg · 90% of one rep max 104.0 kg
Method and assumptions
1RM = W × ((1+r/30) + 36/(37−r) + r^0.10)/3 Mean of Epley W(1+r/30), Brzycki W×36/(37−r) and Lombardi W×r^0.10; 90% estimate = 0.9×1RM. Epley, Brzycki and Lombardi are estimates from the entered load and repetition count. Their arithmetic mean is a comparison value, not a measured maximum or proof of improved accuracy. Exercise, technique, fatigue and repetition range affect agreement; do not treat the estimate as a safe load to attempt. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Data sources
The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Disclaimer
These calculators are for general information only and are not a medical device, a diagnosis or a treatment plan. Reference ranges describe populations, not individuals, and do not account for pregnancy, medication, disability or athletic training. Discuss your own situation with a qualified healthcare professional.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
1RM = W × ((1+r/30) + 36/(37−r) + r^0.10)/3
- 1RM
- estimated one-rep max (average)
- W
- weight lifted
- r
- reps performed
Mean of Epley W(1+r/30), Brzycki W×36/(37−r) and Lombardi W×r^0.10; 90% estimate = 0.9×1RM.
Frequently asked questions
Why does the calculator average three different one-rep-max formulas?
Epley, Brzycki and Lombardi are estimates from the entered load and repetition count. Their arithmetic mean is a comparison value, not a measured maximum or proof of improved accuracy. Exercise, technique, fatigue and repetition range affect agreement; do not treat the estimate as a safe load to attempt.
Which inputs and limits apply to One Rep Max Calculator?
Use the units shown beside each field. These are form limits, not recommended settings. Weight lifted: 0–1,000 kg; Repetitions completed: 1–20 reps 1RM = W × ((1+r/30) + 36/(37−r) + r^0.10)/3 Mean of Epley W(1+r/30), Brzycki W×36/(37−r) and Lombardi W×r^0.10; 90% estimate = 0.9×1RM. Epley, Brzycki and Lombardi are estimates from the entered load and repetition count. Their arithmetic mean is a comparison value, not a measured maximum or proof of improved accuracy. Exercise, technique, fatigue and repetition range affect agreement; do not treat the estimate as a safe load to attempt. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
What is a complete worked example for Weight lifted = 100 kg; Repetitions completed = 5 reps?
Inputs: Weight lifted = 100 kg; Repetitions completed = 5 reps. Calculation: 1RM = W × ((1+r/30) + 36/(37−r) + r^0.10)/3. Results: Epley = 116.7 kg; Brzycki = 112.5 kg; Lombardi = 117.5 kg; Average estimate = 115.5 kg; 90% of one rep max = 104.0 kg.