1RM Calculator: Find Your One Rep Max

The calculator estimates your one rep max (1RM) with the Epley formula and turns it into working weights for strength, muscle and technique sets.

The Epley formula is 1RM = weight × (1 + reps ÷ 30). Lift 100 kg for 5 reps and your estimated max is 100 × (1 + 5 ÷ 30), about 117 kg. A single rep is taken as your max. GymDroid uses the same formula in the app, so the number you see here is the number you see there.

It is closest when the set is between 3 and 8 reps and taken close to failure with good form. Above 10 reps the error grows, because endurance starts to matter more than strength. Treat the result as a planning number, not a target to test every week.

Around 85 percent for strength work in sets of 3 to 5, around 75 percent for muscle growth in sets of 8 to 10, and around 65 percent for technique and higher rep work. The chart above rounds each weight to the nearest 2.5 kg so you can load it on a bar.

GymDroid takes the same number and sets your starting weights for every exercise in the plan, then adjusts them from what you log. Pick a plan below and read week 1 here.

Do a hard set of 3 to 8 reps with good form, then multiply the weight by 1 plus the reps divided by 30. That is the Epley formula this calculator uses.

Both give similar results between 2 and 10 reps. Epley reads slightly higher at mid range reps, Brzycki slightly lower. What matters most is using the same formula every time so your numbers compare.

Sets of 3 to 5 reps give the most accurate estimate. Sets of up to 8 are still useful. Past 10 reps the estimate becomes a rough guess.

For most lifters an estimate is enough and carries less risk. If you do test a single, warm up well, use safety bars or a spotter, and stop the session if your form breaks down.