Bicep Curl Max Calculator

The barbell curl is where a one rep max is least useful and most interesting — useful because it tracks arm strength over time, interesting because it is exactly the kind of lift where the classic formulas are known to be off. Enter a strict set below; 66 lb goes in as 30 kg.

Worked example

66 lb (30 kg) for 10 strict reps:

• Epley: 30 × (1 + 10 ÷ 30) = 40.0 kg, about 88 lb
• Brzycki: 30 × 36 ÷ (37 − 10) = 40.0 kg, about 88 lb

They match to the decimal, and not by coincidence: 10 reps is the single point where the two equations cross. Change the reps in either direction and the answers split apart again.

Light lifts are where the formulas break down

Both equations convert repetitions into load at a fixed rate — Epley divides by 30, Brzycki effectively by 36 — regardless of what you are lifting. A 2026 preprint tested that assumption against 303,494 near-failure sets across 388 exercises and found the rate should not be fixed at all: it should fall as the load gets lighter, because on a light lift each additional rep carries more information about your true maximum.

The example the authors give is a curl. For a 29 lb (13 kg) dumbbell curl taken to 10 reps, Brzycki predicts a max near 37 lb (17 kg), while their weight-dependent version predicts about 49 lb (22 kg). On a 220 lb (100 kg) bench press for 5 reps, the same two methods land within 5 lb of each other. The disagreement is not random — it grows as the weight falls, and it is largest for light exercises taken to high rep counts, which describes most curl sets.

So read the number above as a floor rather than a point estimate, and do not compare it against a training partner’s curl calculated some other way.

Strict reps, or nothing to measure

There is no bar to be pinned under here, which is precisely why the reference set drifts. The failure mode is the cheat curl: the torso starts swinging, the hips generate the load, and the rep count climbs while biceps involvement falls. That inflates the estimate and loads the lumbar spine in a position it did not sign up for. Keep the elbows in place and the ribcage still, and end the set at the first rep that needs body English.

The same math on the big lifts

• Bench press max calculator
• Squat max calculator
• Deadlift max calculator
• Overhead press max calculator

To see how the two equations differ across the whole rep range, read Epley vs Brzycki; to average them on any lift, use the one rep max calculator.