One Rep Max Calculator
The one-rep max is the gold standard for measuring strength, but attempting a true 1RM carries injury risk. The Brzycki formula lets you estimate it safely from a submaximal set, then calculates percentage-based training weights.
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Formula
1RM = Weight ÷ (1.0278 − 0.0278 × Reps)
The Brzycki formula models the linear decline in the maximum weight you can lift as repetitions increase. The denominator (1.0278 − 0.0278 × reps) decreases as reps go up, so the estimated 1RM rises. The formula is most accurate for 2–10 rep sets and less reliable above 10 reps, where fatigue factors become non-linear.
How to use the One Rep Max Calculator
- 1
Enter your weight lifted
Value should be in lbs.
- 2
Enter your repetitions performed
Value should be in reps.
- 3
Read your results instantly
Results update in real time as you type.
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Why test or estimate your 1RM
Most strength programs prescribe loads as percentages of your 1RM. Knowing your 1RM for squat, bench press, and deadlift lets you follow percentage-based programming precisely. A true 1RM test requires a spotter, a thorough warm-up, and carries some injury risk. Estimating from a heavy submaximal set — typically 3–8 reps to near-failure — gives you a useful working number with much lower risk. Re-test every 4–8 weeks to track progress and update your training weights.
Using percentage-based training
Periodized strength programs typically prescribe work at 65–85% of 1RM for hypertrophy, 85–95% for strength, and above 95% for peaking. The 90% and 80% values this calculator provides cover the most common training zones. For example, 5×5 programs usually use 80–85% of 1RM for working sets. Knowing these numbers removes guesswork and prevents undertraining (too light) or overtraining (too heavy) on any given session.
Tips & Insights
Use 3–5 rep sets for accuracy
The Brzycki formula is most accurate when you perform 3–5 heavy reps to near-failure. Higher rep sets (8+) introduce more fatigue variability and reduce formula accuracy.
Rest fully before your test set
To get a reliable submaximal estimate, rest 3–5 minutes before your test set and ensure it is a true maximal effort for that rep count, not a conservative submaximal set.
Track across exercises
Calculate 1RM estimates for all your main lifts and record them. Comparing ratios (e.g., deadlift to squat) can reveal muscular imbalances worth addressing in programming.
Worked Examples
185 lbs for 5 reps
Estimated 1RM ≈ 208 lbs; 90%: 187 lbs; 80%: 167 lbs
135 lbs for 8 reps
Estimated 1RM ≈ 169 lbs; 90%: 152 lbs; 80%: 135 lbs
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Frequently Asked Questions
Is the Brzycki formula accurate?
It is accurate to within 5% for most people performing 3–8 rep sets. Accuracy decreases at higher rep counts because neural and metabolic fatigue becomes a larger factor.
Should I ever attempt a true 1RM?
Experienced lifters with good technique can attempt a true 1RM with a qualified spotter. Beginners should rely on formula estimates for the first 1–2 years of training.
How often should I recalculate my 1RM?
Every 4–8 weeks is typical for active strength athletes. Recalculate after any extended break from training to reset your training percentages appropriately.
Can I use this for all exercises?
Yes — the formula works for any barbell or machine exercise. It is most commonly applied to squat, bench press, deadlift, and overhead press.
What does training at 80% of 1RM feel like?
At 80% of 1RM, most people can complete 6–8 clean reps before failure. It should feel challenging but technically clean — not a grind from the first rep.
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