One Rep Max Calculator
Estimate your 1RM and training loads
Estimate your one-rep max from a set you've done, then see suggested training weights at 70%, 80% and 90%.
How the estimate works
Whether you call it a 1rm calculator or a max lift calculator, the arithmetic is one multiplication.
This uses the Epley formula, the most widely used of several published options:
1RM = weight × (1 + reps ÷ 30)
The logic is that each additional rep you can complete implies roughly 3.33% more strength in reserve. It is a linear approximation of a relationship that is not quite linear, which is exactly where its limits come from.
Lift safely. Use a spotter, safety bars and clean form when working near maximal loads, and stop if form breaks down.
Estimated 1RM from a 225 lb set
| Reps at 225 lb | Estimated 1RM | 90% | 80% | 70% |
|---|---|---|---|---|
| 1 | 233 lb | 209 | 186 | 163 |
| 3 | 248 lb | 223 | 198 | 173 |
| 5 | 263 lb | 236 | 210 | 184 |
| 8 | 285 lb | 257 | 228 | 200 |
| 10 | 300 lb | 270 | 240 | 210 |
| 12 | 315 lb | 284 | 252 | 221 |
| 15 | 338 lb | 304 | 270 | 236 |
Look closely at the first row. Enter one rep at 225 lb and Epley returns 233 lb — more than a weight you demonstrably just lifted for a single. That is not a bug; the formula multiplies by (1 + 1/30) regardless, and it was never fitted for single-rep inputs. If you genuinely did one rep, your 1RM is the weight you lifted. Use the formula for sets, not singles.
Why the rep range matters so much
| Reps | Multiplier | Reliability |
|---|---|---|
| 1 | ×1.033 | Do not use — you already know your max |
| 3 to 8 | ×1.10 to ×1.27 | Most reliable |
| 10 | ×1.333 | Usable |
| 12 to 15 | ×1.40 to ×1.50 | Overstates for most lifters |
| 20 | ×1.667 | Not meaningful |
Above about ten reps, muscular endurance rather than maximal strength becomes the limiting factor, and the two do not track each other. A lifter who can grind out 20 reps is demonstrating a different quality from one who fails at 3, and Epley cannot tell them apart — it just keeps multiplying. Sets of 3 to 8 are where the estimate is worth having.
Individual variation matters too. Some lifters are naturally "grinders" who manage many reps at a high percentage of max; others are explosive and fail quickly. The same formula misjudges both in opposite directions.
Programming with percentages
| Goal | % of 1RM | Typical reps |
|---|---|---|
| Peaking, maximal strength | 90 to 95% | 1 to 3 |
| Strength | 80 to 90% | 3 to 6 |
| Hypertrophy | 65 to 80% | 8 to 12 |
| Endurance, technique | 50 to 65% | 15+ |
- Round to the nearest plate rather than chasing the exact number. 236 lb becomes 235.
- Estimates differ by lift. The relationship is tighter on squat and deadlift than on bench, and less reliable still on isolation work.
- Re-estimate every few weeks. A percentage calculated three months ago is programming for a weaker version of you.
- Estimate from a set you finished with clean form, at or one rep shy of failure. A set that broke down halfway gives a number that is neither safe nor useful.
Estimating instead of testing
A true one-rep max attempt is fatiguing and carries real injury risk, particularly without a spotter, safety bars or several years of practice under heavy loads. Estimating from a set of 3 to 8 gives a figure close enough for programming at a fraction of the risk, and it can be done inside a normal training session rather than as an event.
Competitive lifters test for a reason — they need a verified number on a given day. For everyone else, the estimate is the more sensible tool, and the honest framing is that it is a planning figure with a few percent of error rather than a fact about your body.
How this one rep max calculator works out its numbers
Uses the Epley formula: 1RM = weight × (1 + reps ÷ 30). Training loads are 90%, 80% and 70% of that estimate.
- Reliable for 3 to 8 reps, usable to about 10, and increasingly optimistic beyond that. Above ten reps the limiting factor shifts from maximal strength to muscular endurance, which the formula cannot distinguish.
- Not valid at 1 rep. Epley applies its multiplier regardless, returning 233 lb for a 225 lb single. If you completed one rep, that weight is your max.
- Other formulas exist — Brzycki, Lombardi, O'Conner — and give slightly different answers. Epley is the most widely used and sits mid-range.
- Assumes a clean set to or near failure. A set with broken form or several reps in reserve produces a misleading figure.
- Individual variation is real. Lifters differ in how many reps they can complete at a given percentage of max, so treat the output as a planning figure with a few percent of error.
Reviewed September 2026.
Figures reviewed . Every worked example on this page is checked against the calculator above.
One Rep Max Calculator: frequently asked questions
How do I calculate my one rep max?
The Epley formula is weight × (1 + reps ÷ 30). Five reps at 225 lb estimates a 263 lb max. It is most reliable for sets of 3 to 8 reps.
How accurate is an estimated 1RM?
Good for sets of 3 to 8 reps, usable to about 10, and increasingly unreliable above that. Above ten reps muscular endurance becomes the limiting factor rather than maximal strength, and the two do not track each other.
Why does the calculator give a higher number than my actual single?
Because Epley multiplies by (1 + reps ÷ 30) regardless of the input, so one rep at 225 lb returns 233 lb. The formula was never fitted for single-rep inputs. If you lifted it once, that weight is your max.
How many reps should I use to estimate my 1RM?
Three to eight, with clean form, at or one rep shy of failure. Very high-rep sets overstate the result — 15 reps applies a 1.5× multiplier, which few lifters' actual strength supports.
Should I actually test my 1RM?
Usually not. A true max attempt is fatiguing and carries real injury risk without a spotter, safety bars and experience. Estimating from a submaximal set gives a number close enough for programming at far lower risk.
What percentage of 1RM should I train at?
90 to 95% for peaking, 80 to 90% for strength, 65 to 80% for hypertrophy, and 50 to 65% for endurance and technique work. Round the resulting loads to the nearest available plate.
Is the 1RM formula the same for every lift?
No. The rep-to-max relationship is tighter on squat and deadlift than on bench press, and less reliable again on isolation exercises. Treat cross-lift comparisons with caution.
How often should I re-estimate my max?
Every four to six weeks while training consistently. Percentages calculated months ago are programming for a weaker version of you, which quietly turns a strength block into maintenance work.