One-rep max calculator
Estimate your one-rep max for any lift using the weight and reps from a recent set, with a full percentage training table.
What is one-rep max (1RM)?
Your one-rep max is the heaviest weight you can lift for a single, complete repetition with good form. It's the reference point strength programs are built around — rather than picking training weights arbitrarily, you can express every set as a percentage of that number, which makes programs comparable across lifters of very different strength levels.
Why train with percentages of your 1RM
A percentage-based target automatically scales to you: "80% for 5 reps" means something different — and appropriately challenging — for every lifter, unlike a fixed weight prescription. It also makes it easy to plan intensity across a training block: heavier percentages for strength phases, lighter percentages with more volume for hypertrophy.
The Epley formula explained
This calculator estimates 1RM using the Epley formula: 1RM = weight × (1 + reps ÷ 30). It assumes each additional rep you complete below failure represents roughly the same fractional increase in how far you were from your true max — which holds up well for low-to-moderate rep sets, but gets noisier as rep counts climb, since fatigue accumulates differently from person to person.
Safety tips for estimating your max
- Use a recent, honest set. The formula is only as good as the input — a set taken to true near-failure gives a far better estimate than a set stopped early.
- Prefer 3–6 rep sets for estimating. This range balances accuracy with safety, without needing to approach an actual 1RM attempt.
- Don't test a true 1RM without a spotter. If you do want to attempt an actual single, do it under supervision with proper safety equipment.
- Re-estimate periodically, not every session. Chasing week-to-week fluctuations in an estimate leads to overtraining more often than it leads to useful data.
Frequently asked questions
How accurate are one-rep max calculators?
Formula-based estimates are generally accurate within about 5–10% for sets of 1–10 reps. Accuracy drops for higher rep sets (12+), since fatigue affects the relationship between reps and load differently for each lifter.
Which formula does this calculator use?
This calculator uses the Epley formula: 1RM = weight × (1 + reps ÷ 30), one of the most widely used estimation formulas in strength training.
Should I actually test my 1RM instead of estimating it?
For most training purposes, an estimate is safer and sufficient. Testing a true 1RM carries higher injury risk and is usually reserved for experienced lifters under proper supervision.
Does this formula work for any exercise?
It works best for compound barbell lifts like the squat, bench press, and deadlift, where the Epley formula was originally validated. It becomes less reliable for isolation exercises, machines, or lifts with a lot of technical variation, since fatigue and leverage don't scale with reps the same way.
Why do estimates get less accurate above 10 reps?
Every 1RM formula assumes a fairly direct relationship between reps and fatigue. Past about 10–12 reps, that relationship breaks down — some lifters can grind out 20 reps at a weight others fail at 15, so the same rep count no longer maps to the same percentage of max as reliably.
How should I use the percentage table in training?
Most strength programs are written as a percentage of 1RM — for example, "5 sets of 5 at 80%." Once you have an estimated 1RM, the table converts those percentages into an actual weight to load on the bar, so you don't have to do the math mid-session.
Will my 1RM change over time?
Yes — consistently, as you get stronger. Re-test or re-estimate every 4–8 weeks of consistent training so your percentage-based programming stays accurate; using a stale 1RM will make your working sets feel progressively easier (or harder, if you plug in outdated numbers after a layoff).