One Rep Max Calculator

What this tool does

The One Rep Max Calculator estimates the heaviest single lift you could manage from a weight and rep count, using seven published formulas including Epley and Brzycki. It rounds to loadable plates and lists training loads from 50 to 100 percent of your max with typical rep ranges.

Many strength programmes prescribe loads as a percentage of your one-rep max (1RM), the heaviest weight you can lift once with good form. Testing a true max is fatiguing, takes careful warm-ups and carries some risk, especially for newer lifters. Estimating it from a heavier set of a few reps is a safer everyday alternative.

This calculator applies seven formulas: Epley (w × (1 + r/30)), Brzycki (w × 36 ÷ (37 − r)), Lander, Lombardi, Mayhew, O'Conner and Wathan. They agree closely at low reps and drift apart as reps rise, so the default shows their average along with the full spread. Loads can be rounded to 2.5 kg or 5 lb steps so the training table matches what you can actually put on the bar.

How to use One Rep Max Calculator

1. Enter the weight you lifted and choose kilograms or pounds.
2. Enter the number of reps you completed with good form, ideally close to failure.
3. Choose the main formula, or keep the average of all seven.
4. Turn plate rounding on or off.
5. Read your estimated 1RM, the formula range and suggested 5-rep and 10-rep working weights.
6. Use the percentage table to set loads for your programme and download it as CSV.

Tips for better results

• Use sets of 3 to 6 reps for the most reliable estimates.
• Re-estimate every four to six weeks as you get stronger.
• Keep separate estimates for each lift; squat, bench press and deadlift respond differently to rep ranges.

Common use cases

• Setting percentages for programmes such as 5/3/1 or linear progression plans.
• Tracking strength progress without regular max testing.
• Choosing warm-up and working loads before a session.
• Comparing the strength of training partners using different rep schemes.

Common mistakes to avoid

• Using a set of 15 or more reps, where estimates become unreliable.
• Entering a set stopped well short of failure, which underestimates your max.
• Treating the estimate as a target to attempt without spotters or safety bars.