100% free · Runs 100% in your browser · No signup needed
Safety first: this is an estimate for programming training percentages, NOT an instruction to attempt the load. Testing a true one-rep max carries injury risk. Never attempt maximal lifts alone — always use a spotter and appropriate safety equipment.
Formulas: Epley (1985): w×(1+reps/30) · Brzycki (1993): w×36/(37−reps) · Lombardi: w×reps0.1. Estimates are most accurate from 2–10 reps performed to near failure; all formulas break down past ~12 reps.
Try an example: 100 kg × 5 reps
Your one-rep max - the heaviest weight you can lift for a single repetition - is the cornerstone number of serious strength training. Almost every proven program expresses its working weights as percentages of 1RM: 85 percent for heavy triples, 70 percent for volume work, 90 percent for peaking. But actually testing a true 1RM is exhausting, risky and disruptive to training. Our free One-Rep Max Calculator estimates it safely from a submaximal set you have already done, using three classic, research-backed formulas side by side.
Enter the weight you lifted and how many clean reps you managed, and the tool instantly shows the Epley, Brzycki and Lombardi estimates plus their average - your working 1RM figure. Below that, a training-percentage table converts the estimate into ready-to-use loads at 90, 80 and 70 percent, so you can walk into your next session with exact numbers instead of guesswork. Both kilograms and pounds are supported.
Strength training is only half the equation - the other half is fuel. Pair your 1RM programming with our TDEE Calculator to find the calories that support your training, and the Macro Calculator to dial in the protein that rebuilds the muscle you break down.
The calculator applies three of the most cited 1RM prediction formulas in strength science, each derived from observed relationships between submaximal reps and maximal strength:
Epley (1985): 1RM = weight x (1 + reps / 30). Simple and widely used; slightly generous at higher rep counts.
Brzycki (1993): 1RM = weight x 36 / (37 - reps). The most conservative of the three for mid-range reps, and a favourite in research settings.
Lombardi: 1RM = weight x reps^0.1. An exponential model that tracks Epley closely in the sweet spot.
All three agree best when your input set is 2 to 10 reps taken close to failure - a hard set of 5 tells the formulas far more than an easy set of 15. Past about 12 reps, every formula degrades because endurance, not maximal strength, becomes the limiting factor; the tool is designed around honest, near-maximal efforts in the low-to-mid rep range. Showing all three estimates side by side is deliberate: when they cluster tightly, you can trust the number; when they spread, treat the average cautiously. The averaged figure becomes your working 1RM, and the percentage table underneath translates it into training loads - 90 percent for heavy strength work, 80 percent for moderate volume, 70 percent for technique and hypertrophy blocks. Runners building leg strength can cross-check conditioning with our Running Pace Calculator, and anyone tracking body composition should keep an eye on our BMI Calculator.
The reason the formulas insist on near-failure sets is simple: they extrapolate from fatigue. A set stopped five reps short of failure tells the math almost nothing about your limit, while a set stopped one rep short reveals it clearly. That is also why honest rep counting matters so much - two sloppy half-reps logged as full reps will inflate every formula equally. When your input is truthful and hard, the three estimates converge; when it is generous, they diverge, and that divergence itself is useful feedback telling you to retest with a heavier, cleaner set.
Suppose you bench-pressed 100 kg for 5 clean reps, stopping one rep shy of failure. Here is exactly what each formula returns:
Epley: 100 x (1 + 5/30) = 100 x 1.1667 = 116.7 kg
Brzycki: 100 x 36 / (37 - 5) = 3,600 / 32 = 112.5 kg
Lombardi: 100 x 5^0.1 = 100 x 1.1746 = 117.5 kg
The three estimates cluster between 112.5 and 117.5 kg, and their average is about 115.6 kg - a sensible working 1RM. Your training table then writes itself: 90 percent is roughly 104 kg for heavy triples and doubles, 80 percent is about 92.5 kg for sets of 6-8, and 70 percent is near 81 kg for volume or technique work. Notice that Brzycki, the conservative one, sits a few kilos below the others - if you are programming a peaking block where overshooting is costly, many lifters deliberately use the Brzycki figure alone. Try your own best recent set in the calculator and see how your numbers line up.
A non-negotiable safety note, straight from the research brief: this tool gives you an estimate for programming training percentages - it is not an instruction to attempt the load. Testing a true one-rep max carries genuine injury risk, especially on bench press and squat, and you should never attempt maximal lifts alone. Always use a competent spotter, safety bars or a power rack, warm up thoroughly, and remember that the calculator exists precisely so you can train intelligently without ever needing to find out what your absolute limit is the hard way.
For sets of 2-10 reps to near failure, all three land within a few percent of most lifters' true max, and Epley and Lombardi usually agree closely. Brzycki tends to be the most conservative. No formula beats an actual well-prepared test - but the whole point of the calculator is to avoid needing one.
Each was derived from different lifter populations and different mathematical models of fatigue. The spread is a feature, not a bug: it shows you the uncertainty band. Use the average for general programming and the lowest figure when being conservative matters.
You can enter it, but treat the result sceptically. Beyond about 12 reps, muscular endurance dominates and all three formulas overestimate maximal strength. For the most reliable estimate, retest with a heavier weight in the 3-8 rep range.
The formulas work best for the big barbell lifts - squat, bench press, deadlift, overhead press - where technique is stable. They are less reliable for highly technical Olympic lifts or machine exercises with variable resistance curves.
Round down, especially early in a program. Plates come in fixed jumps anyway, and starting a touch light leaves room to build momentum. You can always add weight next week; you cannot un-tweak a shoulder.
Yes, with a little extra caution. Enter the total weight lifted (both dumbbells combined, for example) and the formulas work the same way. Just remember that stabiliser fatigue on dumbbell work can make high-rep sets less predictive, so keep inputs in the 3-8 rep range for the most trustworthy estimates.
Every 4-8 weeks, or whenever a working set starts feeling clearly easier than the percentages suggest. Beginners may need more frequent updates; advanced lifters can stretch it to a full training block.
Serious about strength? Serious lifters document their journey. FistHost shared hosting starts at just $0.99 per month, and every annual plan includes a free domain name - launch your training log, coaching site or powerlifting club page on fast hosting with free SSL and one-click installs.
Thousands of creators trust FistHost to keep their sites fast and online. Grab an annual plan today, claim your free domain, and put your progress where the world can see it.
No reviews yet. Be the first to review this tool!
Reviews are protected by captcha and moderated before they appear.