This one rep max calculator estimates the heaviest weight you could lift for a single repetition, based on a set you have actually performed. Enter the weight and how many reps you completed, and it applies the two most widely used estimation formulas — Epley and Brzycki — then builds your training percentage table.
Knowing your 1RM matters even if you never plan to test it: nearly every serious strength program (5/3/1, Starting Strength progressions, Sheiko, powerlifting peaking blocks) prescribes working weights as percentages of your max. Estimating it from a 5-rep set is safer than maxing out and accurate enough for programming.
The Formulas
The two standards, with weight w and reps r:
- Epley: 1RM = w × (1 + r/30)
- Brzycki: 1RM = w × 36 / (37 − r)
Example — you bench 225 lbs for 5 reps:
- Epley: 225 × (1 + 5/30) = 262.5 lbs
- Brzycki: 225 × 36 / 32 = 253.1 lbs
The two agree almost exactly at 2–5 reps and drift apart as reps climb; the truth is usually between them. Both assume the set was taken to (or very near) failure — a comfortable set of 5 with three reps in the tank underestimates your max.
How Accurate Are 1RM Estimates?
Accuracy depends mostly on the rep count you estimate from:
- 2–5 reps: typically within 2–3% of a tested max — the sweet spot
- 6–10 reps: within roughly 5% for most lifters
- 11–15 reps: increasingly unreliable — muscular endurance starts driving performance more than maximal strength
Accuracy also varies by lift and lifter. Estimates run truest on compound barbell lifts (squat, bench, deadlift) and are less reliable for isolation exercises. Experienced lifters tend to slightly beat their estimates on deadlifts and fall short on strict overhead presses.
Using Training Percentages
The percentage table is where the number becomes useful:
- 85–95%: low-rep strength work (1–5 reps) — the range that builds maximal force
- 70–80%: the classic hypertrophy zone (6–12 reps)
- 60–70%: volume, technique work, and warm-ups
Two practical rules: recalculate your 1RM every 4–8 weeks as you progress, since stale percentages quietly turn a program too easy; and when a program says “80% for 5 reps,” that percentage refers to your current estimated max, not an aspirational one. Round working weights to the nearest 5 lbs (2.5 kg) — barbell math beats false precision.
Frequently Asked Questions
How do I calculate my one rep max without maxing out?
Take a weight you can lift for 2–10 clean reps close to failure, then apply an estimation formula. The Epley formula — weight × (1 + reps/30) — is the most common. For example, 185 lbs for 8 reps estimates to 185 × (1 + 8/30) ≈ 234 lbs. Lower rep counts give more accurate estimates.
Is it safe to test a true one rep max?
For healthy, experienced lifters with good technique, an occasional tested max with a spotter and proper warm-up is reasonably safe. Beginners should not test true maxes — form breaks down under maximal load before they have the technique to protect their joints and spine. Estimated maxes serve the same programming purpose with none of the risk.
Which is more accurate, Epley or Brzycki?
They are nearly identical up to about 5 reps. Beyond that, Epley tends to run slightly high and Brzycki slightly low, with the true value usually in between. Research does not crown a consistent winner across all lifts and populations, which is why this calculator shows both.
What percentage of my 1RM should I train at?
It depends on the goal: 85–95% for maximal strength (1–5 reps), 70–80% for muscle growth (6–12 reps), and 60–70% for endurance, technique, and warm-up work. Most well-designed programs rotate through these zones rather than living in one.
Why is my calculated max higher than what I can actually lift?
Formulas assume the input set was taken to genuine failure, that you are practiced at heavy singles, and that the lift is a big compound movement. If your set had reps in reserve, or you rarely handle near-maximal weights, your tested max will lag the estimate — the skill of grinding out a true single is itself trainable.