One Rep Max Calculator (1RM) — Epley, Brzycki & Lombardi 🌎

What 1RM actually represents

One-rep max is the heaviest load you can complete for one rep with technique a judge would pass: full depth on a squat, pause and lockout on bench, no hitching or downward movement on a deadlift. It's the single number that anchors most strength programming — Wendler's 5/3/1 calls it your training max (typically 85–90% of true 1RM), Sheiko expresses sets as %1RM, Westside programs max-effort days off it. Outside the platform, the practical use is the %1RM chart: you set today's 5×5 at 80%, your top single at 92%, your speed work at 60%. The estimate doesn't need to be precise to 1 lb — it needs to be in the right zip code so your prescribed loads challenge the right energy system.

The three formulas this calculator uses — math worked

All three prediction equations take two inputs: w (weight lifted) and r (clean reps completed at near-failure, RPE 9+). They're regression models fit to test-retest bench-press and squat data and still hold up.

Epley (1985):     1RM = w × (1 + r / 30)
Brzycki (1993):   1RM = w × 36 / (37 − r)
Lombardi (1989):  1RM = w × r^0.10

The calculator reports all three plus their average, which is the number you should use — averaging cancels each model's individual bias. For r = 1 every equation collapses to w (the weight you actually lifted, no estimation needed). For r > 10 the formulas progressively overpredict, especially Epley, which is a linear extrapolation.

Worked example: 225 lb × 5 reps

A classic gym benchmark — two plates per side on bench or squat for a clean set of 5.

Spread between high and low is about 11 lb (≈4%). That's normal — under a 5% spread, just take the average and move on.

%1RM training table off a 260 lb 1RM

Reps-to-1RM percentage reference

A quick way to sanity-check the output: a clean set to RPE 9–10 roughly corresponds to this % of 1RM.

Accuracy by rep range — what the studies show

LeSuer et al. (1997) in the Journal of Strength and Conditioning Research tested Epley, Brzycki and other equations against true-tested 1RMs in bench, squat and deadlift on 67 trained college athletes. Bench predictions were within ~3% across the board. Squat and deadlift showed slightly higher error. Takeaway: pick an approach, stay consistent across training blocks.

Best practice based on the literature:

Three other published equations exist if you want to cross-check by hand: O'Conner (1989): 1RM = w × (1 + 0.025 × r); Lander (1985): 1RM = (100 × w) / (101.3 − 2.67123 × r); Mayhew (1992): 1RM = (100 × w) / (52.2 + 41.9 × e^(−0.055 × r)). They land within a few pounds of the three above for sets of 3–10 reps.

Why your gym 1RM might differ from the prediction

The formulas were calibrated on standardized testing — rested lifter, full warm-up, monitored technique, an RPE 9–10 set. Real-life misses:

How to actually use this for programming

1. Do a top set of 3–6 reps at RPE 9. Last rep should be a grinder. Don't go to failure — leave the bar moving.
2. Plug w and r in. Take the average across the three formulas, not Epley alone.
3. Subtract 10% for your training max if you're running 5/3/1 (Wendler's rule — builds in cushion for bad days).
4. Set the %1RM table off your training max. This is the load you actually use Monday/Wednesday/Friday.
5. Re-estimate every 4–8 weeks when a 5RM or 3RM PR lands, or at the end of a block.
6. Don't chase 1RM weekly. It's a benchmark, not a daily metric.

Limitations and edge cases