One Rep Max (1RM) Calculator

What Is a One-Rep Max?

Your one-rep max (1RM) is the heaviest weight you can lift once with full range of motion and acceptable form. It's the standard yardstick of maximal strength — programs prescribe loads as percentages of it, and tracking it over months is the cleanest measure of strength progress. This calculator estimates your 1RM from a submaximal set, so you don't have to test it under a barbell.

The Formulas Behind the Estimate

This tool uses the two most validated equations, where w is the weight lifted and r the reps completed:

• Epley: 1RM = w × (1 + r ÷ 30)
• Brzycki: 1RM = w × 36 ÷ (37 − r)

They agree closely up to about 10 reps and diverge beyond that — which is also where all rep-based estimates lose accuracy, because sets of 12+ test endurance more than strength. For best results, use a recent set of 3–6 hard reps taken close to failure.

Worked Example

You bench press 100 kg for 5 clean reps:

• Epley: 100 × (1 + 5/30) = 116.7 kg
• Brzycki: 100 × 36 ÷ (37 − 5) = 112.5 kg

Your true max likely sits in the 112–117 kg band. Program off the conservative end if in doubt.

Training Percentages: What to Lift for Each Goal

% of 1RM	Typical reps	Primary adaptation
90–100%	1–3	Maximal strength, neural drive
80–90%	3–6	Strength with some muscle growth
67–80%	6–12	Hypertrophy (muscle size)
50–67%	12–20+	Muscular endurance, technique volume

If your program calls for "5 sets of 5 at 75%", multiply your estimated 1RM by 0.75 — from the example above, roughly 85–87 kg.

Estimated vs Tested Max

Estimates are accurate to within roughly ±5% for experienced lifters on big compound lifts — and they're safer, faster and less fatiguing than true max testing. Genuine 1RM attempts belong in specific contexts (powerlifting meets, end-of-block testing) with a spotter or safety pins, a thorough ramp-up, and no grinding through form breakdown. Most lifters get everything they need from estimates updated every 4–6 weeks.

Lift-specific quirks: the deadlift tends to estimate high from rep sets (grip and back fatigue limit reps), while machine lifts estimate more reliably than free weights. Track estimates per exercise rather than assuming carryover. To fuel strength training properly, see our protein calculator and calorie calculator — strength gains come notably easier at maintenance calories or a small surplus.

Frequently Asked Questions

How often should I test or re-estimate my 1RM?

Re-estimate from a hard set every 4–6 weeks — frequent enough to keep training percentages honest, infrequent enough not to disrupt training. True max-out sessions are best limited to a few times a year, typically at the end of a training block.

Why is my squat 1RM estimate less accurate than my bench?

Estimates assume the limiting factor is the target muscles, but squats and deadlifts are often limited by bracing, grip or positional endurance during rep sets. Lifts with more technical or stability demands deviate more — use lower-rep sets (3–5) for those estimates.

Can beginners use 1RM percentages?

Loosely. Novices' strength changes week to week and their grinding form near failure is unreliable, so percentage-based programming fits awkwardly. Most beginner programs sidestep this with linear progression — adding small amounts of weight each session — until progress stalls.

Is it safe to actually test my one-rep max?

With safeties or a competent spotter, a proper warm-up ramp, and the discipline to refuse ugly reps, max testing is reasonably safe for healthy, experienced lifters. Skip it if you're new (under ~6 months of consistent training), returning from injury, or training alone without safety pins.