One Rep Max Calculator

Estimate your 1RM from a set you've lifted — no risky max attempt needed. Includes a training percentage table.

kg (or lb — units don't matter)

1 to 12 reps

Please enter a valid weight and reps between 1 and 12.

Estimated 1RM
—
your estimated single-rep maximum
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What is a one-rep max?

Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition of an exercise — like the squat, bench press, or deadlift — with proper form. It's the gold-standard measure of maximal strength and the reference point for planning training loads. Rather than attempting a risky maximal lift, this calculator estimates your 1RM from a set you can already complete.

The Epley formula

This tool uses the Epley formula, one of the most established 1RM equations:

  • 1RM = weight × (1 + reps ÷ 30)

For example, lifting 100 kg for 5 reps estimates a 1RM of 100 × (1 + 5/30) = about 116.7 kg. Because units cancel out, you can enter kilograms or pounds — the result comes back in the same unit.

Training percentages

Once you know your 1RM, you can program your workouts as a percentage of it. The table in your result shows common loads. As a rough guide:

  • 90–95% — maximal strength, 1–3 reps
  • 80–90% — strength, 3–5 reps
  • 70–80% — hypertrophy (muscle growth), 6–10 reps
  • 60–70% — endurance and technique, 10–15 reps

Tips for an accurate estimate

Use a set taken close to failure (leaving 0–2 reps in reserve) for the best estimate, and keep it in the 1–10 rep range — accuracy falls off beyond about 12 reps because endurance starts to matter more than pure strength. Always warm up thoroughly and prioritise form over numbers.

Frequently asked questions

What is a one-rep max (1RM)?

Your one-rep max is the maximum weight you can lift for a single repetition of an exercise with good form. It's the standard measure of maximal strength and is used to set training loads as a percentage of that max.

How is 1RM calculated without testing it?

This calculator uses the Epley formula: 1RM = weight × (1 + reps/30). By entering a weight you lifted for several reps, it estimates the single-rep maximum without the risk of attempting a true max lift. Accuracy is best at 1–10 reps.

How accurate is the estimate?

Rep-based 1RM estimates are usually within about 5% of a true tested max when using sets of 1 to 10 reps. Beyond 10–12 reps accuracy drops sharply because fatigue and endurance, not pure strength, start to dominate.

What are 1RM percentages used for?

Strength programmes prescribe loads as a percentage of your 1RM. For example, sets of 3–5 reps for strength often use 80–90%, while higher-rep hypertrophy work uses 65–75%. The percentage table makes it easy to pick the right weight.

Is it safe to test my actual 1RM?

Testing a true 1RM carries injury risk and should only be done by experienced lifters who are fully warmed up, ideally with a spotter. For most people, estimating from a set of 3–5 reps is safer and accurate enough.

Disclaimer: This calculator provides an estimate for informational purposes only. Lifting heavy weights carries injury risk. Warm up properly, use correct form, and consult a qualified coach if you're unsure.

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