Why guess your max when you can estimate it?
Maxing out is a pain. You need a spotter, a good warm-up, and a day where you actually feel like grinding through a near-fatal single. Most of the time you just want a number to plan your week around. That’s what this does. Tell it a set you already crushed, say 100 kg for 5 reps, and it works backward to what you could probably hit for one.
Two formulas run side by side. Epley and Brzycki are the two most-cited estimators in strength training, and they rarely agree exactly. That’s fine. The gap between them is small at low reps and tells you how much to trust the number. The calculator also shows the average, which is the figure most lifters end up using for programming.
The two formulas
Here’s the actual math, no hand-waving:
- Epley: 1RM = weight x (1 + reps / 30)
- Brzycki: 1RM = weight x 36 / (37 - reps)
Both were fit to real lifting data decades ago. Epley tends to read slightly higher on big rep sets; Brzycki climbs fast as you approach its ceiling (it literally breaks at 37 reps, since the denominator hits zero). Inside the useful range, 1 to about 10 reps, they land within a couple of percent of each other.
Do a single rep and there’s nothing to estimate. The weight on the bar is your max, so the tool just reports it and builds the percentage table off that.
The percentage chart is the useful part
A 1RM number on its own is bragging rights. The training table is where it earns its keep. Once you have an estimated max, the tool spits out what 95%, 90%, 85% and so on down to 60% look like in actual kilos or pounds, next to the rep range you’d typically grind at each load.
Running a 5x5 program? You’re living around 80 to 85%. Speed work and explosive triples sit up near 90%. Hypertrophy blocks park in the 65 to 75% zone for higher reps. Instead of doing percentage math in your head between sets, you read it off the chart and load the bar.
How accurate is this, really?
Honest answer: close enough for programming, not gospel. Rep-max estimators assume you took the set near failure with clean form. Leave four reps in the tank and the estimate undershoots. Grind a set with terrible technique and it overshoots. They also drift the higher your reps go, a 20-rep set is a cardio test as much as a strength one, so anything you build off it is shaky.
Treat the average as a planning anchor. Retest with a real heavy single every few weeks if you care about the exact figure. And never load a calculated max onto the bar and send it cold. Work up to it.
Common questions
Which formula should I trust, Epley or Brzycki?
Neither alone. Use the average. If you only want one, Brzycki is slightly more conservative at typical rep counts, which is safer for loading.
What rep count gives the best estimate?
Three to five reps. Low enough that the formulas stay tight, high enough that you’re not actually maxing out to get the input.
Can I plug in a set I didn’t take to failure?
You can, but the result will read low. The formulas assume the last rep was a real struggle. Leaving reps in reserve means your true max is higher than the estimate.
Does it work in pounds and kilos?
Both. Flip the unit toggle and every number, including the whole training chart, switches with it.
Why does the chart show rep ranges next to each percentage?
So you can match a percentage to the kind of work you’re programming. 85% is a heavy triple or set of five; 65% is higher-rep volume. It saves you cross-referencing a separate loading table.