One Rep Max Calculator
Estimate your true single-rep max from any working set, and see exactly what to lift at every training percentage.
Strength Tools → One Rep Max Calculator
One rep max calculator
Enter a weight and rep count from a recent set.
Training percentages based on your estimated max
| % of 1RM | Weight | Typical use |
|---|
How this calculator works
A one rep max, or 1RM, is the most weight you can lift for a single clean rep before your form breaks down. It’s the number lifters use to plan almost everything else — what weight to use for a set of 5, what “80% intensity” actually means in kilos, whether a program is asking too much of you this week. The problem is that testing it directly is exhausting, and if you’re not experienced with a true max attempt, it’s genuinely one of the easier ways to get hurt in a gym.
So instead of grinding through an actual single-rep max, most lifters estimate it from a set they can complete safely — say, five reps at a weight that’s hard but manageable — and let a formula do the rest. That’s what this calculator does. You tell it what you lifted and how many reps you got, and it works backward to estimate what your true single-rep max would be.
The formula behind the number
This tool uses the Epley formula, one of the two most widely trusted methods for estimating 1RM from a multi-rep set, and the one that tends to hold up best for rep ranges under about ten:
Here’s what that looks like with real numbers. Say you bench press 100kg for 5 reps. Plug that into the formula: 100 × (1 + 5 ÷ 30) = 100 × 1.167 = 116.7kg. That’s your estimated one rep max — not a number you’ve actually lifted, but a solid, evidence-based prediction of what you could lift for one clean rep on a good day.
Epley vs. Brzycki: why this calculator uses Epley
If you’ve spent any time researching 1RM calculators, you’ve probably come across a second formula called Brzycki. Both are legitimate, both are used in strength research, and both will give you a very similar number for moderate rep ranges. The difference shows up at the edges:
| Formula | Best for | Where it drifts |
|---|---|---|
| Epley | Rep ranges of 1–10, most general training use | Slightly overestimates above 12 reps |
| Brzycki | Lower rep ranges, close to true max attempts | Becomes unreliable and can even predict a lower max as reps rise past 10 |
Epley tends to be the more forgiving, broadly applicable choice for the rep ranges most training programs actually use, which is why it’s the default here. If you’re testing at very low reps (1–3) close to your actual max, both formulas will land close enough together that the difference won’t matter for programming purposes.
How to use your 1RM percentages in training
The percentage table this calculator generates isn’t just a novelty — it’s the actual bridge between “I estimated my max” and “I know what to load the bar with today.” Strength-focused training blocks are almost always written as a percentage of 1RM rather than a flat number, because it scales automatically to your current strength instead of assuming everyone lifts the same weight.
- 85–100%: near-max singles and doubles, used sparingly, usually only in peaking phases.
- 70–85%: the range most strength programs live in — sets of 3 to 6, built to add weight to the bar over time.
- 60–70%: hypertrophy-focused volume work, higher reps, more total fatigue per session.
- 50–60%: warm-up territory, or technique work on a day you’re not pushing intensity.
Common mistakes with 1RM estimates
The single biggest mistake is testing an actual max alone, without a spotter, just to double-check what a calculator already told you. It’s not worth the risk — that’s precisely the situation this tool exists to help you avoid. Estimates also lose accuracy past 10–12 reps, since fatigue affects a 15-rep set very differently than it affects a 5-rep set, and no formula fully accounts for that. And finally, don’t confuse a good day with your actual max — an estimate made from a fresh, well-rested set will usually read a bit higher than one made after a hard training week, which is completely normal and not a sign anything’s wrong with the math.