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One-Rep Max Calculator

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Estimate your one-rep max (the heaviest weight you could lift for a single rep) from a weight and rep count you've already performed — no need to actually attempt a maximal lift to get a useful estimate.

One-Rep Max Calculator

Live
Estimated 1-rep max
234.3
Brzycki formula
229.7
85% (working weight)
199.2
Most accurate under about 10 reps. Same units in, same units out (works for lb or kg).

The formulas

Epley: 1RM = weight × (1 + reps ÷ 30) Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Example

185 lb for 8 reps — Epley: 185 × (1 + 8/30) ≈ 234.3. Brzycki: 185 × 36/(37−8) ≈ 229.7. The two formulas typically land close together, with the true value likely somewhere in that range.

Step-by-step guide

  1. Enter the weight you lifted and how many clean reps you completed with good form.
  2. Read both formula estimates — they'll usually be close but not identical.
  3. Use the 85% figure as a rough estimate of a solid working weight for strength-focused sets.

Common mistakes

Using a set taken to failure with poor form near the end — these formulas assume the reps were completed with good technique throughout.
Trusting the estimate for very high rep counts (15+) — these formulas become progressively less reliable the further the set is from a near-maximal effort.

Frequently asked questions

Should I actually test my true 1RM?

Testing a true 1RM carries injury risk, especially without a spotter or coach, and isn't necessary for most training goals. This estimate is a safer, practical alternative for programming purposes.

Why do Epley and Brzycki give slightly different numbers?

They're both empirical formulas fit to different datasets, so small differences are expected. Neither is definitively "more correct" — treating the two together as a reasonable range is a sensible approach.

How is this used for programming training weights?

Many strength programs prescribe working sets as a percentage of estimated 1RM — for example, "3 sets of 5 at 80% of 1RM" — which this calculator can help you translate into an actual weight.

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