One Rep Max Calculator
Plug in a set you've already done and I'll estimate your 1 rep max, no risky max-out needed.
Fill in the form and your result lands here.
Learn the details
How it's figured
Your one-rep max (1RM) is estimated with the Brzycki formula: 1RM = weight ÷ (1.0278 − 0.0278 × reps). It is most accurate for sets of 1-10 reps and less reliable beyond that.
Use a set of 3-5 reps for the closest estimate. Retest every 4-8 weeks to update your working percentages.
Why it's an estimate
Your one rep max is the heaviest weight you could lift for a single clean rep, estimated here from a set you have already done instead of tested by loading the bar until you fail. It is mainly there to pick your working weights, so treat it as a close neighborhood rather than a number exact to the pound.
What a 1 rep max actually is
Your one rep max, or 1RM, is the heaviest weight you could lift for a single clean rep on a given lift. Testing it directly means loading the bar until you fail, which is fatiguing, eats into your training week, and carries real injury risk if your form breaks down under a true max attempt. Estimating it from a set you have already done well gets you a number that is close enough to plan around, without any of that risk. That is what the calculator above does.
The formula behind the estimate
This calculator runs the Brzycki formula: weight times 36, divided by (37 minus reps). The idea is that each additional rep at a given weight represents a predictable slice of your true max. Your result also shows Epley, weight times (1 plus reps divided by 30), which models that slice slightly differently. The two agree almost exactly around 10 reps but drift apart at lower rep counts, where Epley reads several pounds higher, and neither style of estimate should be trusted much beyond 12 to 15 reps, since fatigue stops behaving in a straight line that far out.
A worked example
Say you squat 225 pounds for a clean set of 5 reps. Brzycki, the formula this tool uses, puts that at 225 times 36, divided by 32, which comes out to about 253 pounds. Epley would call the same set 225 times 1.167, landing at roughly 262 pounds, about 9 pounds higher. Either way the message is the same, your true single is somewhere in that neighborhood, not a value to treat as exact to the pound.
Working percentages
- About 95%: a heavy single or double
- About 85%: a solid set of 5
- About 70 to 75%: hypertrophy work in the 8 to 12 rep range
Those bands are the practical use for your estimated 1RM, picking working weights for a given rep target without guessing. Keep in mind the estimate itself gets less reliable the higher the rep count you plug in to generate it. A 1RM estimated from a set of 3 is on firmer ground than one estimated from a set of 15.
What to do with your number
Use your estimated 1RM to set training loads, not as a score to chase. Pair it with your RPE and percentage calculator to pick a weight for a target rep and effort, your training max to build a program around a slightly conservative number, and your warmup calculator to build up to your working sets without wasting energy. If you want the estimate explained from the top, without the formulas, how to calculate your one-rep max walks it through in plain terms. Retest every few weeks as you get stronger and let the number move with you.
Reps to 1RM percentage chart
Roughly how many reps you can get at each percentage of your max. Your numbers will vary a little, so use it as a starting point.
| Reps | % of 1RM |
|---|---|
| 1 | 100% |
| 2 | 97% |
| 3 | 94% |
| 4 | 92% |
| 5 | 89% |
| 6 | 86% |
| 7 | 83% |
| 8 | 81% |
| 9 | 78% |
| 10 | 75% |
| 11 | 72% |
| 12 | 69% |
Brzycki formula, rounded to the nearest whole percent.
Questions people ask
- 01How accurate is a one rep max calculator?
- Close enough to plan training around, not exact to the pound. This tool runs the Brzycki formula, and a different formula, Epley, can land several pounds higher on the same set, especially at lower rep counts. Treat the number as a close neighborhood for setting working weights, and let a set of 3 to 5 reps give you a firmer estimate than a set of 12 or more.
- 02Why do different 1RM calculators give different numbers?
- They run different formulas. Brzycki, used here, and Epley agree closely around 10 reps but drift apart at lower rep counts, with Epley reading a bit higher. Neither should be trusted much past 12 to 15 reps, since fatigue stops behaving in a straight line that far out and both formulas start guessing more than estimating.
- 03What percentage of my 1RM should I train with?
- Roughly 95% for a heavy single or double, 85% for a solid set of 5, and 70 to 75% for hypertrophy work in the 8 to 12 rep range. Those bands are the practical use for an estimated 1RM: picking a working weight for a rep target without guessing, not a score to test directly.
- 04Is it safe to test my actual one rep max?
- It carries more risk than estimating one, since loading the bar until you fail is fatiguing, eats into your training week, and raises the odds of your form breaking down under a true max attempt. Estimating from a set you have already done well gets you close enough to plan around without that risk, which is what this calculator is for.
- 05How often should I retest my 1RM?
- Every 4 to 8 weeks, or whenever your working sets start feeling light. Re-estimating from a fresh set of 3 to 5 keeps your percentages honest.
- 06Which rep range gives the most accurate estimate?
- Sets of 3 to 6 reps. Past about 10 reps, endurance starts to matter more than strength, so the estimate drifts.