One Rep Max (1RM) Calculator
Estimate the most weight you could lift for a single repetition from a multi-rep set, and see your training loads as a percentage of that 1RM.
Last updated: June 20, 2026 · Medically reviewed by TG we-Calculate Editorial TeamUnit
kg
reps
Epley estimate of the heaviest weight you could lift for a single rep.
- 1
Rep factor (reps ÷ 30)
5 ÷ 30 = 0.1667 - 2
Epley multiplier (1 + rep factor)
1 + 0.1667 = 1.1667 - 3
Estimated 1RM
100 × 1.1667 = 116.7Epley formula: 1RM = weight × (1 + reps ÷ 30).
How do you calculate your one-rep max?
Use the Epley formula: one-rep max equals the weight lifted multiplied by (1 + reps ÷ 30). For example, lifting 100 kg for 5 reps estimates a 1RM of about 117 kg. A single all-out rep is already your 1RM, and accuracy is best at 10 reps or fewer.
Formula
How this is calculated
The calculator takes two inputs: the weight you lifted (in kilograms or pounds — the unit is just a label and never changes the maths) and the number of repetitions you completed in that set to or near failure. It then applies the Epley equation, 1RM = weight × (1 + reps ÷ 30). The reps ÷ 30 term is a fixed empirical factor: each extra rep you manage adds roughly 1/30th (about 3.3%) of the lifted weight onto the estimated single-rep maximum, because the more reps you can do at a given load, the further that load sits below your true ceiling.
A special case is handled explicitly: at exactly 1 rep the result is the weight itself, since a single all-out lift is already your 1RM and no estimation is needed. Inputs are validated — weight must be positive and reps must fall between 1 and 12.
Key assumptions and limits: the set should be taken close to muscular failure, and accuracy is best from 1 to about 10 reps. Beyond that, fatigue, technique and rep-speed vary too much, so the estimate drifts. The percentage table below simply scales the same 1RM (95% down to 70%) to show typical training loads.
Examples
| Input | Result |
|---|---|
| 100 kg × 5 reps (Epley) | ≈ 116.7 kg estimated 1RM |
| 60 kg × 10 reps (Epley) | ≈ 80 kg estimated 1RM |
| 140 kg × 1 rep | 140 kg (a single rep is already your 1RM) |
About this calculator
A one-rep max (1RM) is the heaviest weight you can lift for a single repetition of an exercise. Testing a true 1RM directly carries injury risk, so lifters usually estimate it from a comfortable multi-rep set. The Epley formula (1985) does this with 1RM = weight × (1 + reps ÷ 30) and is one of the most widely used estimators; Brzycki and Lombardi are common alternatives that give very similar results in the 1–10 rep range.
Once you know your estimated 1RM, training programmes prescribe loads as a percentage of it: heavy strength work sits around 85–95%, hypertrophy work around 70–80%. The percentage table below shows those loads with the approximate number of reps each one allows, so you can plan working sets without re-testing your max every session.
Frequently asked questions
It is most accurate for sets of about 1 to 10 reps. As the rep count rises, fatigue and technique vary more, so estimates beyond 10 reps become less reliable.
They are two different prediction equations. Epley uses 1RM = weight × (1 + reps ÷ 30); Brzycki uses weight ÷ (1.0278 − 0.0278 × reps). Both give very similar results for low rep counts.
A single maximal repetition is by definition your one-rep max, so no estimation is needed. The Epley formula only predicts a 1RM when you perform more than one rep.
Also known as
Sources & references
TG we-Calculate Editorial Team. (2026). One Rep Max (1RM) Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/one-rep-max-calculator
TG we-Calculate Editorial Team. "One Rep Max (1RM) Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/one-rep-max-calculator.
TG we-Calculate Editorial Team, "One Rep Max (1RM) Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/one-rep-max-calculator
@misc{wecalculate_one_rep_max_calculator, title = {One Rep Max (1RM) Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/one-rep-max-calculator}}, year = {2026}, note = {TG we-Calculate} }
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