What is One-Rep Max Calculator?

The One-Rep Max Calculator estimates the heaviest weight you can lift for one rep, based on a lighter set you've already done. It runs your numbers through Epley, Brzycki, and Lombardi formulas so you don't have to risk a true max attempt.

The calculator runs five formulas at once (Epley, Brzycki, Lombardi, O'Conner, and Mayhew) so you can compare and average them rather than trusting any single curve. It then prints a percentage table from 60% to 100% in 5% steps, which is what most strength programs (5/3/1, Texas Method, Stronglifts) use to prescribe working sets. Estimates are most accurate at 1–6 reps and degrade past 10.

How to use

1. Enter the weight you lifted and the number of reps you completed in your set.
2. Select your preferred estimation formula or compare results across all formulas.
3. View your estimated 1RM along with percentage-based training loads for programming your workouts.

When to use

• Programming next week's working sets at the right percentage of your max.
• Estimating a new 1RM after a top set without doing an actual single.
• Comparing two lifters' relative strength when they tested at different rep ranges.

Result

You bench pressed 185 lbs for 6 reps. Using the Epley formula, your estimated 1RM is approximately 216 lbs. You can then plan training sets at 70% (151 lbs) for hypertrophy or 90% (194 lbs) for strength.

FAQ

How accurate are 1RM estimates from rep-max formulas?

Within about 5% for sets of 3–6 reps for most trained lifters. Past 10 reps the curves diverge significantly because muscular endurance becomes the limiter, not maximal strength. For competition prep, only a real tested max is reliable.

Why do the five formulas give different numbers?

Each was fitted on different populations and lifts. Epley and Brzycki tend to agree at 2–10 reps. Lombardi is more conservative for high reps. Mayhew was built from bench-press data on football players. Average them or take the median for a balanced number.

Should I use lbs or kg?

Either, the math works on any unit as long as you stay consistent. Toggle to lbs if you train in pounds; results come back in lbs. Switch to kg for plates marked in kilos. The percentages don't change between units.

Can I estimate a 1RM from a heavy single?

Yes, enter 1 rep and the weight you actually lifted. All five formulas return that exact weight, because at 1 rep the input is the max. Useful when you want the training-load table for a recently tested max.

Is rep-max calculation safe for beginners?

It's actually safer than testing an actual 1RM, because you only need to go heavy enough for 3–6 clean reps. Most coaches recommend new lifters use estimates rather than maxing out, since form breakdown at true singles is a common cause of injury.

Related Tools