One-Rep Max (1RM) Calculator
Your estimated one-rep max is the weight you lifted × (1 + reps ÷ 30). Lifting 100 kg for 5 reps gives an estimated 1RM of about 116.7 kg.
Estimated one-rep max
116.7 kg
Training percentages
95%
111 kg
90%
105 kg
85%
99 kg
80%
93 kg
75%
88 kg
70%
82 kg
65%
76 kg
60%
70 kg
50%
58 kg
Show the math
- 1
Divide your reps by 30
5 ÷ 30 = 0.1667
The Epley formula estimates how much a multi-rep set 'discounts' the weight compared with a true single rep.
= 0.1667
Read the steps as text
- Divide your reps by 30. 5 ÷ 30 = 0.1667 The Epley formula estimates how much a multi-rep set 'discounts' the weight compared with a true single rep.
- Add 1, then multiply by the weight lifted. 100 × (1 + 0.1667) = 116.7 This is the Epley formula: 1RM = weight × (1 + reps ÷ 30).
How a one-rep max is estimated
Testing a true one-rep max — the most you can lift for a single rep — is fatiguing and carries some injury risk, especially for lifts like the squat or deadlift. Instead, most lifters estimate it from a lighter set taken close to failure, using a formula built on the relationship between weight and reps completed.
This calculator uses the Epley formula, one of the most widely used: 1RM = weight × (1 + reps ÷ 30). It's reasonably accurate up to about 10–12 reps; beyond that, fatigue and technique breakdown make any formula's estimate less reliable, so this calculator caps input at 15 reps.
Using the training percentage table
Many strength programs prescribe work as a percentage of 1RM rather than an absolute weight, since it scales automatically as you get stronger. The table above converts your estimated 1RM into common training percentages — for example, 70% is a typical weight for higher-rep volume work, while 90%+ is reserved for low-rep strength work.
Because this is an estimate, retest periodically (ideally with an actual near-max set) rather than treating the number as fixed — technique, sleep and how fresh you are on test day all shift the real number.
Frequently asked questions
- How accurate is an estimated one-rep max?
- Generally within a few percent of your true max for sets of 10 reps or fewer taken close to failure. Accuracy drops for higher rep counts, which is why this calculator caps input at 15 reps.
- What's the Epley formula?
- 1RM = weight × (1 + reps ÷ 30). It's one of several similar formulas (others include Brzycki and Lombardi) that all estimate a true max from a lighter, higher-rep set.
- Should I actually test my one-rep max?
- Not necessary for most lifters. Testing a true 1RM is fatiguing and adds injury risk, especially without a spotter. Most training programs work just as well from an estimated max.