How the estimate is calculated
The calculator uses the Epley formula, the same one Kilos uses for its estimated one rep max charts and records, so the numbers here match the app:
1RM = weight × (1 + reps ÷ 30)A set of 100 kg for 5 reps gives 100 × (1 + 5 ÷ 30) = 116.7 kg. The percentage table runs the same formula backwards: at 80 percent of that, 93.3 kg, it predicts about 8 reps.
How accurate is it?
- Best from 2 to 10 reps. A hard set in that range says the most about your strength. Past about 12 reps, how long you can keep going matters more than how strong you are, and the estimate drifts.
- One rep adds about 3 percent. The formula is applied as is, also at one rep. If you really lifted the weight once, that weight is your one rep max.
- Use a set taken close to failure. A set you stopped with five reps left in the tank underestimates you.
- Other formulas give other numbers. Brzycki, weight × 36 ÷ (37 − reps), gives 112.5 kg for 100 kg × 5 where Epley gives 116.7 kg. Neither is exact; what matters is using the same one every time, which is why this page uses the app’s.
Using the percentage table
Programs often give weights as a percentage of your one rep max. The table turns your estimate into those weights, with the reps the formula predicts you could do at each. As a rule of thumb, heavy strength work sits around 80 to 90 percent for 3 to 6 reps, and muscle building work around 65 to 80 percent for 6 to 12. You do not need to test a true max to use it: an estimate from a hard set of 3 to 6 is safer and close enough to plan with.
Tracking it over time
One estimate is a snapshot. The useful number is the trend: if your estimate for the same lift rises over weeks, you are getting stronger, even when the weights you use change. Kilos works this out for every set you log and draws it per exercise. Want to load the bar for one of the weights above? The plate calculator shows the plates per side.