One Rep Max Calculator
Estimate your 1RM and training loads from a weight and reps.
Formula
About this calculator
Your one-rep max (1RM) is the most weight you can lift for a single repetition of an exercise, and it is the foundation of most strength-training programs. Testing a true 1RM is risky and fatiguing, so lifters estimate it instead from a set taken with a lighter weight — which is exactly what this calculator does.
It uses two of the most established prediction equations. The Epley formula estimates 1RM as the weight lifted multiplied by one plus the reps divided by thirty; the Brzycki formula uses the weight times thirty-six divided by thirty-seven minus the reps. The two agree closely at low reps and diverge slightly at higher ones, so the tool shows both plus their average for a balanced figure.
Once you know your estimated 1RM, the training-load table becomes a programming cheat sheet. It converts your max into the weights that correspond to common percentages — for example, roughly 80% for sets of eight or 90% for sets of four — so you can load the bar correctly for strength, hypertrophy or power work without guesswork.
Accuracy is best when the test set is about ten reps or fewer; beyond that, fatigue and form breakdown make estimates less reliable. Always warm up thoroughly, use proper technique and, when lifting anywhere near maximal loads, work with a spotter or in a rack with safety pins.
Frequently asked questions
How accurate is a 1RM calculator?
Very reasonable for sets of about ten reps or fewer. This tool averages the Epley and Brzycki formulas; accuracy drops as the rep count climbs because fatigue affects performance.
Which formula should I trust?
Both are well established. Epley and Brzycki agree closely at low reps, so the average shown here is a sensible single figure to work from.
How do I use the percentage table?
It converts your estimated 1RM into training loads. Pick the percentage that matches your goal — heavier percentages for strength, lighter for hypertrophy — and load the bar to that weight.
Is it safe to test my actual 1RM?
Only with proper warm-up, good form and a spotter or safety rack. Estimating from a submaximal set is safer and, for most lifters, accurate enough.
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⚠️ 1RM estimates are for training guidance only. Lifting near-maximal loads carries injury risk; warm up, use proper form and a spotter, and progress gradually.