ClutchCalcs

Exercise

One Rep Max (1RM) Calculator

Programming your training around percentages of 1-rep max is the gold standard for strength work — 5×5 at 80%, 3×3 at 90%, deload at 60%. Problem is, actually testing your 1RM is brutal, risky, and you only want to do it every 8-12 weeks. The fix: estimate your 1RM from a set you actually did. This calculator runs three of the most validated rep-max formulas (Epley, Brzycki, Lombardi) and averages them to give you a reliable estimate, then prints out training weights at common percentages (60-95%) with their typical rep ranges. Best accuracy at 3-8 reps; estimates drift high above 10 reps.

The three formulas (and what they assume)

All rep-max formulas estimate 1RM from a set taken to (or near) failure. We average three of the most widely-validated formulas:

  • Epley: 1RM = weight × (1 + reps/30). Most forgiving at higher reps.
  • Brzycki: 1RM = weight × 36 / (37 - reps). Best for 1-10 reps; breaks down above 10.
  • Lombardi: 1RM = weight × reps^0.10. Splits the difference between the two.

Worked example: a working set of 225 lb × 5 reps on bench press. Epley = 225 × (1 + 5/30) = 262.5. Brzycki = 225 × 36/32 = 253. Lombardi = 225 × 5^0.10 = 264. Average estimated 1RM = 260 lb. Real-life test would likely land in the 255-265 range — within 5% is the accepted accuracy band.

Training percentages and typical rep ranges

  • 95% 1RM: 2-3 reps. Heavy singles/doubles. Peaking phases.
  • 90% 1RM: 3-5 reps. Strength work, low-rep sets.
  • 85% 1RM: 5-6 reps. Classic strength range (Wendler 5/3/1, Texas Method).
  • 80% 1RM: 6-8 reps. Strength-hypertrophy mix.
  • 75% 1RM: 8-10 reps. Hypertrophy work.
  • 70% 1RM: 10-12 reps. Volume/hypertrophy.
  • 65% 1RM: 12-15 reps. High-volume hypertrophy or deload.
  • 60% 1RM: 15+ reps. Endurance or warm-up work.

How to use this calculator

  1. Weight lifted: the working weight on a set taken close to failure (1-2 reps in reserve).
  2. Reps performed: the actual rep count on that set. Don't pad it — if you got 5 with maybe 1 more in the tank, enter 5.
  3. Output: estimated 1RM and a percentages table from 60-95% with corresponding weights and rep ranges.
  4. Re-test every 4-8 weeks as you progress — program off the new max.

Common scenarios

Intermediate lifter, 5x5 squat program, hit 275x5 today. Estimated 1RM = 318 lb. Next cycle, program 5x5 at 80% = 255 lb (close to current working weight), heavy singles at 90% = 285 lb on test days. Add 5 lb every 1-2 weeks as long as 5x5 stays clean.

Powerlifter prepping for meet, hit 405x3 deadlift. Estimated 1RM = 446 lb. Meet opener (90%) = ~400, second attempt (95%) = ~425, third attempt = something you grind out. The 1RM estimate is the planning baseline.

Hypertrophy block, want to know what 8 reps should feel like on bench. If your bench estimated 1RM is 225, 75% = 170. Program 4 sets of 8 at 165-170 lb. If you blow through 8 reps with 3 in reserve, you're stronger than the formula says — retest with a heavier 3-5 rep set.

FAQ

Does this work for all lifts? +
Reasonably well for compound lifts (squat, bench, deadlift, OHP, row). Less accurate for isolation lifts (bicep curls, leg extensions) where stabilizers and form variance matter more. Not great for explosive lifts (clean, snatch) where technical breakdown determines failure more than absolute strength.
I just started lifting. Should I bother with 1RM percentages? +
Probably not yet. Novice linear-progression programs (StrongLifts 5x5, Starting Strength) work by adding weight every session rather than programming off percentages. You'll outgrow 1RM-based programming in your first 3-6 months. After that, programs like 5/3/1, Texas Method, and intermediate splits use percentages of an estimated 1RM as the foundation.
Should I actually test my 1RM directly? +
Periodically, yes — every 8-16 weeks during a peaking block or meet prep. Direct tests are more accurate than estimates, but they're also fatiguing and slightly risky. For week-to-week programming, estimates are plenty accurate. Powerlifters and Olympic weightlifters test directly because the sport requires it.
What's RIR (reps in reserve)? +
Reps in reserve = how many more reps you could have done before failure. RIR 0 = absolute failure. RIR 2 = could have done 2 more. Modern hypertrophy research suggests RIR 1-3 sets produce similar results to RIR 0 with less recovery cost. When using this calculator, the formulas assume RIR 0 — if you stopped with reps in reserve, your true 1RM is higher than the estimate suggests.
Why is Brzycki's formula best for 1-10 reps? +
Brzycki was specifically derived from data in the 1-10 rep range. Above 10 reps the formula's denominator (37 - reps) approaches zero too fast and estimates become unreliable. Epley is gentler at high reps but slightly under-predicts at low reps. Averaging compensates for both.
Can I use this for body weight exercises? +
Sort of — but body weight exercises (pull-ups, push-ups, dips) often have very high rep capacity at body weight, which puts you outside the formulas' accuracy range. For weighted pull-ups or weighted dips at low reps, yes, the formulas work normally on the added weight + bodyweight.
Why is my actual 1RM lower than this estimate? +
Two common causes: (1) you didn't go all the way to failure on the input set (which is fine), or (2) maximal-effort technique differs from your working-set technique — nerves, brace, setup all add to a fresh peak attempt. Real 1RM testing involves a slow ramp-up with progressively heavier singles; you can't just walk up and pull 1RM cold.
What's a deload week? +
Reduction in training volume or intensity (typically 60-70% of normal load) for one week every 4-8 weeks to allow recovery and supercompensation. Use the percentages table for deload work — 60% 1RM × same set/rep scheme is a clean deload that keeps technical work without grinding.