MariposasOne-Rep Max Calculator
By Zachary, builder of Mariposas · Reviewed against published exercise-science sources (references)
· Last updated June 2026
Strength | % of 1RM | Weight (lb) |
|---|---|
| 95% | 110 |
| 90% | 104 |
| 85% | 98 |
| 80% | 92 |
| 75% | 87 |
| 70% | 81 |
Enter a weight and the reps you hit, and this calculator estimates your one-rep max using the Epley, Brzycki and Lombardi formulas, then prints a full percentage table so you can program your working sets. Estimates are most accurate at 1-10 reps.
How it works
Three separate formulas run in parallel here, each with its own approach to projecting a theoretical one-rep max from a submaximal set. The Epley formula, probably the most widely cited, calculates 1RM as weight multiplied by (1 plus reps divided by 30). Brzycki takes a slightly different angle, dividing the lifted weight by (1.0278 minus 0.0278 times reps), which tends to be a bit more conservative and often tracks well for intermediate lifters who are efficient at grinding near-maximal loads. Lombardi uses an exponential curve, multiplying weight by reps raised to the power of 0.10, and generally produces higher estimates on longer sets. Running all three together matters because no single formula is universally superior across different body types, fiber compositions, and training histories. Seeing where they agree narrows the uncertainty; a wide spread between them is a signal to treat the number as a rough anchor rather than a precise ceiling.
When to use it
This tool is especially useful for lifters who want to run a percentage-based program, such as 5/3/1 or any conjugate or linear periodization template, without actually grinding a true one-rep max attempt. Testing a real max has a cost: it's taxing on the nervous system, it carries injury risk at the extreme end of effort, and most coaches don't recommend doing it more than a few times a year. Athletes coming back from a layoff, beginners building their first training max, or anyone mid-cycle who needs to recalibrate their working weights without interrupting the program all get a practical anchor from the percentage table the calculator prints.
Worked example
Say you squatted 225 pounds for 8 clean reps on a day when you had one or two reps left in the tank. The Epley formula yields roughly 285 pounds, Brzycki comes in around 283, and Lombardi lands slightly higher near 290. A reasonable working estimate to base programming on is somewhere in the 283 to 285 range. From there, the percentage table tells you that 70 percent of that estimated max is about 199 pounds, which might be your target load for a higher-volume hypertrophy day, while 85 percent lands around 242 pounds for a strength-focused set. The key thing to understand is that your rep set was at 8 reps with reps in reserve, so the estimate already has some cushion built in. If you had pushed to absolute failure those numbers would shift upward slightly, but programming conservatively off a near-miss set is usually the smarter call.
Tips for an accurate result
- Use a set where you stopped with one to three reps still available, not a grinder to absolute failure. True failure introduces form breakdown and gives you a shakier data point than a crisp near-miss set.
- Keep reps at or below 10 for the most reliable output. All three formulas start diverging significantly above that range because fatigue and aerobic contribution begin distorting the relationship between reps and max strength.
- Pick a weight you know well on a lift you're technically proficient at. Testing a movement you're still learning skews the number because inefficiency, not strength, limits the set.
- If the three formula outputs are spread more than 15 to 20 pounds apart, that's feedback worth paying attention to. It often means the set was influenced by fatigue, inconsistent bar speed, or rep grinding rather than clean submaximal effort.
- Use the resulting percentage table as a training max, not an ego max. Many experienced lifters deliberately set their training max at 85 to 90 percent of their estimated 1RM to build in room for progress and reduce the likelihood of stalling out early in a program cycle.
Formula & sources: methodology · references.
Now go hit the number Mariposas turns every workout, run and class into progress · collect a cute pet 🐾FAQ
- How accurate are these formulas really?
- Research generally puts the margin of error somewhere between 2 and 5 percent for sets in the 1 to 6 rep range, with accuracy declining as reps climb. At 10 reps the estimate is still useful for programming purposes, but you're working with a wider band of uncertainty. Individual factors like muscle fiber type, training age, and how you respond to fatigue all affect how closely any formula tracks your actual max.
- Should I use the highest or lowest number the calculator gives me?
- Most lifters are better served by the more conservative estimate, particularly when setting a training max for a new program cycle. Starting slightly below your ceiling means your early weeks feel manageable, you build momentum, and you're less likely to hit a wall four weeks in. The aggressive estimate is more useful as a goal number to aim toward by the end of a training block.
- Can I use this for any lift?
- The formulas themselves are lift-agnostic, but they were validated primarily on multi-joint barbell movements like the squat, bench press, and deadlift. They tend to be less predictive on isolation exercises or machines where the strength-endurance profile is different. Using it on a barbell row or overhead press is reasonable; using it on a cable curl is less meaningful.
- My actual 1RM test came out lower than the calculator predicted. What happened?
- A few things can cause this. True maximal effort requires dialing in your bracing, technique, and psychological readiness in a way that a submaximal set doesn't demand. Lifters who are relatively better at volume than at absolute grinding often find their real max undershoots the formula. The reverse is also true: some people, particularly more experienced or neurologically efficient lifters, outperform predictions because they express a high percentage of their max strength under heavy singles.
- How often should I recalculate?
- Recalculating every four to eight weeks, or whenever you notice your rep performance at a given weight has shifted noticeably, keeps your programming percentages anchored to where you actually are. If you're on a structured linear or wave-loading program, the program itself often tells you when to retest. Outside of that structure, a meaningful jump in reps at the same weight is a practical signal that your estimated max needs updating.