1RM Calculator
Estimate your one-rep max for any lift
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Your one-rep max (1RM) is the most weight you can lift for a single repetition. It is estimated from a submaximal set so you can program training loads safely. Epley and Brzycki are accurate up to about 10 reps; use the percentage table to set working weights.
How to use this 1RM calculator
Enter the weight you lifted and how many reps you completed with it, pick a formula — Epley, Brzycki or Lombardi — and press calculate. You can switch between kg and lb at any time. For the most reliable estimate, use a recent hard set of roughly 2–10 reps taken close to failure; the tool then shows your estimated one-rep max plus a percentage table for common rep targets.
How to read your result
Your 1RM anchors every training percentage. Loads at 85% and above (roughly 1–5 reps) build maximal strength, 67–85% (about 6–12 reps) is the classic hypertrophy zone, and lighter loads below about 65% train muscular endurance. The built-in table converts your 1RM into working weights for 2, 3, 5, 8, 10, 12 and 15 reps, so you can plan your next session's loads without guesswork.
The formulas and the science behind them
Epley (1985) estimates 1RM as weight × (1 + reps ÷ 30) and is the most widely used equation in strength research. Brzycki (1993), weight × 36 ÷ (37 − reps), was published by strength author Matt Brzycki and runs slightly more conservative at higher reps. Lombardi uses weight × reps^0.1. All three agree within a few percent when the set is under about six reps.
Limits and practical tips
Every rep-based estimate loses accuracy above roughly 10 reps, so base yours on a heavy set of 10 or fewer. Never attempt a true 1RM without a spotter or safety racks and a thorough warm-up. Your real max also swings day to day with sleep, fatigue and technique. Compare strength across body weights with our Wilks calculator, plan recovery with the protein calculator, and log your training meals in the CaloNote app.
Frequently Asked Questions
- What is a 1RM calculator?
- A 1RM calculator estimates the maximum weight you could lift for a single repetition, based on a weight and rep count you already performed. It lets you gauge maximal strength without attempting a risky true one-rep max.
- How accurate is an estimated one-rep max?
- Estimates are most accurate at lower rep counts, ideally under 10 reps, because the relationship between reps and load becomes less reliable at high reps. CaloNote averages the Epley, Brzycki, and Lombardi formulas to improve consistency.
- How do I use the training percentage table?
- The table converts your estimated 1RM into target weights at each percentage, so you can program sets. For example, strength work often uses 80 to 90 percent of 1RM, while hypertrophy commonly sits around 65 to 80 percent.