One-rep max calculator
You do not need to grind a true max to know your strength. Enter any hard working set and this estimates your one-rep max with the Epley formula, the same estimate IronPack uses for its leaderboards and progression targets.
The formula
1RM = weight × (1 + reps ÷ 30)
A single rep is treated as the max itself. Estimates are most reliable from sets of 3 to 8 reps; past 12 reps the relationship between endurance and max strength loosens, so treat high-rep estimates as a rough guide.
Percentage table
Working backwards from a 1RM for programming: the weight you can lift for each rep count, as a percentage of your max.
| Reps | % of 1RM | Example at 100 kg 1RM |
|---|---|---|
| 1 | 100% | 100 kg |
| 2 | 93.8% | 93.8 kg |
| 3 | 90.9% | 90.9 kg |
| 4 | 88.2% | 88.2 kg |
| 5 | 85.7% | 85.7 kg |
| 6 | 83.3% | 83.3 kg |
| 8 | 78.9% | 78.9 kg |
| 10 | 75.0% | 75 kg |
| 12 | 71.4% | 71.4 kg |
Common questions
How accurate is an estimated 1RM?
Within a few percent for most lifters when estimated from 3 to 8 reps, and it tracks your trend very well, which is what matters for training decisions. Different formulas (Epley, Brzycki, Lombardi) disagree by a couple of percent at most in that range.
Should I actually test my 1RM?
Rarely, and only if it matters to you. True max attempts carry the most injury risk and disrupt a training week. An estimate from a hard set of 3 to 5 gives you nearly the same information for free.
Why does IronPack use Epley?
It is the most widely used estimate, it is transparent, and it behaves sensibly across the 1 to 12 rep range IronPack tracks records in. Every set you log updates your records at each rep count automatically, so you rarely need this page mid-workout.
Stop calculating. Start logging.
IronPack tracks your records at every rep count from 1 to 12 automatically, shows estimated 1RM trends over time, and turns every new record into progress in the game.
Get IronPack free on the App StoreMore free tools: DOTS calculator for pound-for-pound scoring and the plate calculator for loading the bar. See what earning records unlocks in the reward loop.
Last reviewed July 2026. The formula and 1-rep behaviour on this page match the IronPack app (v1.1) exactly.