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One-rep max calculator and working weights

This calculator gives you an estimated one-rep max and working weights for sets of 5, 8, 10 and 12 reps from a single recent set. You never need to attempt a true max to train with the right load.

How it's calculated

Enter the weight you lifted and the number of clean reps you completed (1–15). The calculator uses the Epley formula: estimated 1RM = weight × (1 + reps ÷ 30). For example, 60 kg for 8 reps gives an estimated 1RM of 76 kg.

Working weights reverse the same formula for each target rep count, then take 5% off so you finish with about 1–2 reps in reserve. From the 60 kg × 8 example that gives roughly 62 kg for 5 reps, 57 kg for 8, 54 kg for 10 and 51.5 kg for 12.

Estimates are most accurate from sets of 3–10 reps taken close to failure with good form. Above about 12 reps the error grows, and the formula fits some lifts and people better than others. Treat the result as a starting point and adjust by feel and RPE.

Use your gym's smallest available jump. When every set hits the top of the rep range, move up, as described in the 12-week gym plan.

Frequently asked questions

How accurate is the Epley formula?

It is a reasonable estimate for sets of roughly 3–10 reps but not a precise measurement. Individual results vary with experience, the lift and how close to failure the set was. Use it to choose starting weights, then let your logged reps guide you.

Do I need to test my one-rep max?

No. Most people training for muscle and general strength never need a true max attempt. A hard set of 5–8 reps with good form gives a useful estimate with far less risk and fatigue, and you can repeat it every few weeks to track progress.

Why are the working weights a little lighter than the formula?

The calculator removes 5% so you finish each set with about 1–2 reps left. That keeps form clean and lets you complete several quality sets per session, which is how the plan's double progression is designed to work. If the weight feels too light, move up next session.

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General fitness information, not medical advice. Check with a doctor if you have a medical condition, are pregnant or have an injury.