The One Rep Max (1RM) Calculator estimates the maximum weight you could lift for a single repetition of an exercise, based on a set you performed with a lighter weight for multiple reps. Enter the weight you lifted and how many reps you completed.
The one rep max calculator estimates the heaviest weight you could lift for a single repetition of an exercise — your one-rep max, or 1RM — without you actually having to attempt that maximal lift. You provide a weight you lifted and the number of repetitions you managed before failure, and the calculator uses a proven strength formula to project your true maximum. It also produces a full rep-max table showing the weight you should be able to handle for any number of reps, which is exactly what you need to program your training.
Your 1RM is the single most important number in strength training. It defines your current strength level, it is the reference point for nearly every training program, and tracking it over time is the clearest measure of whether your training is working. But testing a true 1RM is demanding and carries real injury risk, especially for beginners and for anyone training alone. Estimating it from a lighter, safer set gives you almost the same information without the danger.
A one-rep max is the maximum amount of weight you can lift for one complete repetition of a given exercise with proper form. It is specific to each lift — your bench press 1RM, squat 1RM, and deadlift 1RM are all different numbers — and it reflects your maximal strength in that movement at that moment in time. As you get stronger, your 1RM rises; that is the whole point of training for strength.
Because a true maximal attempt is taxing and risky, most lifters rarely test it directly. Instead they estimate it, and the estimate turns out to be remarkably accurate when the rep count is low. The relationship between the weight you can lift and the number of reps you can do with it is well understood, and that relationship is what these formulas capture.
You perform a set to (or near) failure with a submaximal weight — say five reps with 100 kg — and enter both numbers. The calculator applies a strength formula that converts "weight × reps" into an estimated single-rep maximum. It then builds a table projecting the weight you could lift for one rep, two reps, three reps, and so on, each expressed as a percentage of your estimated 1RM.
The estimate is most accurate when the reps used are low — ideally under about 10. The more repetitions you perform, the more factors other than pure strength (muscular endurance, fatigue resistance, technique under fatigue) enter the picture, and the less reliable a 1RM projection becomes. A set of 3–6 reps gives the best balance of safety and accuracy.
This calculator offers three of the most widely used and validated 1RM formulas. They agree closely at low rep counts and diverge more as reps climb, so having all three lets you compare.
1RM = weight × (1 + reps ÷ 30)
Published by Boyd Epley in 1985, the Epley formula is one of the most popular. It scales linearly with reps, so for a set of one rep it returns essentially the weight lifted. With 100 kg for 5 reps, it estimates 100 × (1 + 5/30) = 116.7 kg. Epley tends to give slightly higher estimates than Brzycki at higher rep counts.
1RM = weight × 36 ÷ (37 − reps)
Devised by Matt Brzycki, this formula is based on a percentage table relating reps to intensity. For 100 kg × 5 reps it gives 100 × 36/(37 − 5) = 112.5 kg. Brzycki is a close companion to Epley — the two produce identical results at 10 reps — and it is often preferred for its slightly more conservative estimates. Note that it breaks down as reps approach 37, so it is only meaningful for low-to-moderate rep sets.
1RM = weight × reps0.10
The Lombardi formula uses a power relationship rather than a linear one. For 100 kg × 5 reps it estimates 100 × 50.10 = 117.5 kg. It behaves differently from the other two at higher rep counts and can give higher estimates for large numbers of reps.
Below the estimated 1RM, the calculator shows a table of the weights you should be able to lift for a range of rep counts, each as a percentage of your 1RM. This is the practical payoff of knowing your max. Strength programs are almost always written as percentages of 1RM — "work up to 5 sets of 3 at 85%", for instance — and the table turns those percentages into actual plate loadings for your next session.
As a rough guide, most lifters can perform about 1 rep at 100% of 1RM, 5 reps at roughly 85–87%, 10 reps at about 75%, and 15 reps at around 65%. The exact percentages vary between individuals and between exercises — people are generally able to do more reps at a given percentage on the leg press than on the bench press — but the table gives an excellent starting point.
Once you know your estimated 1RM, you can program your training around it:
Because your 1RM changes as you get stronger, it is worth recalculating it periodically — every few weeks, or whenever a working set feels notably easier. Re-estimating from a fresh submaximal set keeps your training percentages honest without repeatedly grinding out risky maximal attempts.
The reason these formulas work is that there is a stable, well-documented relationship between the percentage of your maximum you are lifting and the number of repetitions you can complete at that load. This is often called the load-repetition relationship or a rep-max continuum. Lift 100% of your max and you get one rep by definition; drop to about 85% and most people manage around five; drop to about 75% and roughly ten reps become possible. The formulas are simply mathematical descriptions of that curve, each fitted slightly differently to the same underlying pattern.
Because the curve is steep and reliable near the top — small changes in load produce predictable changes in reps for the first several repetitions — estimates from low-rep sets are excellent. Further down the curve, individual differences in muscle fiber composition and conditioning cause people to diverge: a lifter with predominantly slow-twitch fibers and good endurance may squeeze out far more reps at 70% than a fast-twitch, power-oriented lifter. That divergence is exactly why the estimate loses precision as the rep count climbs, and why all three formulas agree closely at two or three reps but spread apart at fifteen.
Getting stronger comes down to progressive overload — gradually asking your muscles to do more over time, whether by adding weight, adding reps, adding sets, or improving technique. Your estimated 1RM is the single cleanest way to track whether that overload is actually producing results. A working set that felt brutal two months ago and feels manageable today should show up as a higher estimated max, and if your number is stagnant despite consistent training, that is a signal to change something in your program.
Tracking works best when you keep the conditions consistent. Estimate from the same exercise, with a similar rep range, when you are similarly rested, and the trend line becomes meaningful. Sporadic estimates taken from wildly different rep counts and states of fatigue produce noisy data that is hard to interpret. Many lifters log an estimated max every few weeks from a top set and watch the trend rather than obsessing over any single session.
Once you have a reliable 1RM, percentage-based programming becomes straightforward, and it is how most structured strength programs are written. A classic linear program might have you work at 70% for several weeks, then 75%, then 80%, adding load as your estimated max climbs. Peaking programs for powerlifting drive the percentage up toward 90–95% in the final weeks before a competition while cutting volume, so you arrive fresh and primed for a true maximal attempt.
The rep-max table this calculator produces is the bridge between those percentages and the plates on your bar. Rather than doing the arithmetic by hand for every session, you can read the target weight for your prescribed reps directly. As your max rises, recalculating shifts the whole table upward, keeping every training load correctly scaled to your current strength. This is the practical engine behind consistent, measurable progress in the weight room.
How you should treat your estimated 1RM depends a lot on your training age. For beginners, a true maximal attempt is rarely worth the risk: technique is still developing, and a max effort with imperfect form is where injuries happen. Estimating from a comfortable set of five to eight reps gives a safe, useful number to build a first program around, and beginners get stronger so quickly that the estimate should be refreshed often. For experienced lifters, estimates from very low-rep sets are extremely accurate and align closely with tested maxes, and the rep-max table becomes a precise programming tool. Advanced athletes preparing for a powerlifting meet may still test a true max occasionally, but they use estimates day to day to manage load and fatigue. Whatever your level, the calculator gives you the information a max attempt would — without the barbell pinning you to the bench.
Very accurate at low rep counts. Estimates from sets of 2–5 reps are typically within a few percent of a tested maximum. Accuracy declines as the number of reps increases, because endurance and fatigue resistance start to influence how many reps you can do at a given weight.
All three are reputable. Epley and Brzycki are the most popular and give very similar results at low reps (identical at 10 reps). Lombardi behaves differently at higher rep counts. Many lifters simply average the three or use whichever their program specifies.
Occasionally, experienced and well-trained lifters do, with a proper warm-up and a spotter. For most people, and especially beginners, estimating from a submaximal set is safer and nearly as informative. There is little reason to risk a maximal attempt when an estimate serves the same purpose.
Because each lift uses different muscles and leverages. A large compound lift like the deadlift will have a much higher 1RM than an isolation movement like a biceps curl. Always estimate and track each exercise separately.
Every few weeks, or whenever your working weights start to feel easier, is reasonable. Frequent recalculation keeps your percentage-based training aligned with your current strength without repeatedly attempting true maxes.
This One Rep Max Calculator is provided for educational and general informational purposes. The results are estimates produced by standard strength formulas and will vary from your actual maximum. Lifting heavy weights carries a risk of injury; warm up properly, use correct technique, progress gradually, and use a spotter when attempting near-maximal loads. Consult a qualified coach or medical professional before beginning a new training program.