One-Rep Max (1RM) Calculator

What 1RM is and why estimate it

Your one-rep max (1RM) is the heaviest weight you can lift once with proper form. It’s the canonical measure of maximal strength for a given exercise. Programming intensity in resistance training is almost universally expressed as a percentage of 1RM — say, “5 sets of 5 at 80% 1RM.”

But you don’t usually want to test your 1RM. Testing carries injury risk, requires careful warm-up and spotters, and disrupts the training week. So we estimate it from a sub-maximal lift instead.

The three classic formulas

Epley (1985): 1RM = w × (1 + reps / 30)

Brzycki (1993): 1RM = w × 36 / (37 − reps)

Lombardi (1989): 1RM = w × reps^0.10

Where w is the weight lifted and reps is the number of full reps completed close to failure (RPE 9–10). These are all empirically derived regression equations — they learned the strength-endurance relationship from observed lifts.

When each formula performs best

For most everyday training the spread between them is 3–6%, which is below the noise of intra-session strength variation anyway. We display all three plus the average — if the spread is large (>10%), your reps were probably outside the formulas’ validation range and the estimate should be discarded.

How to take the input lift

1. Warm up thoroughly: 2–3 ramping sets at 40–60% of an estimated 1RM.
2. Pick a weight you can do for 3–8 reps with good form, ending close to failure.
3. Complete the set with a stop on the last rep that’s clearly hard but not failed.
4. Plug weight + reps into the calculator.

If you took the set to failure, count one less rep — true 1RM corresponds to a true RPE 10, but most people log RPE 8–9 even when they think they pushed hard.

% of 1RM training table (intensity zones)

Once you have an estimated 1RM, the calculator shows the load corresponding to standard training intensity zones (50% to 95%). Use them roughly as:

• 50–60%: warm-up sets, technique work, deload weeks
• 65–75%: hypertrophy work for 8–12 reps
• 80–85%: strength work for 4–6 reps
• 90–95%: max-effort doubles and singles

These are rules of thumb. Your individual reps-at-percentage profile is highly trainable and varies by exercise.

Pair with our other tools

• Macro calculator — protein anchor for strength training (1.6–2.0 g/kg).
• BMR & TDEE calculator — daily calorie target.
• Body fat percentage calculator — composition tracking.

When to retest

If you’re a beginner, retest every 4–6 weeks. Intermediate lifters, every 8–12 weeks. Advanced lifters, every 12+ weeks or after a deliberate peaking block. Don’t chase 1RM PRs at the expense of consistent training — long-term progression matters more than any single number.

Privacy

All calculation happens in your browser. We never see, log, or store the lifts you enter. Anonymous events (rep count) go to our privacy-first analytics.