ARC guide
How Accurate Is a 1RM Calculator?
ARC estimates 1RM with three formulas and reports the median plus the spread. It is a planning number, not a tested max.
Direct answer
A calculated 1RM is an estimate from a submaximal set. ARC runs Epley, Brzycki, and Lombardi, then uses the median as the headline. The range is the spread between those formulas. Accuracy is better for 1–10 reps than for long burnout sets.
Key takeaway
Use the median to build a load table. Do not treat any single formula as your true max.
The three formulas
Epley: weight × (1 + reps / 30). Brzycki: weight × 36 / (37 − reps). Lombardi: weight × reps^0.10. If you entered a single, the estimate is that weight.
These equations disagree more as reps rise. That is why the product shows a range. Plate rounding (2.5 kg or 5 lb) is applied so the table matches what you can load.
What it is for
Programming percentages, choosing a starting top set, and comparing sessions. It is not a substitute for a well-spotted tested max, and it does not know your fatigue, technique, or equipment.
Example
225 lb for 5 reps produces three slightly different estimates. ARC prints all three, headlines the middle value, and builds 95–60% loads from that median.
Common mistake
Taking a 12–15 rep set to failure and trusting a 1RM equation built around lower reps. Stay in the 1–10 range this tool is designed for.
Use the ARC tool
Run the numbers instead of guessing from the article alone.
How ARC treats this
- Epley, Brzycki, and Lombardi are named prediction equations. ARC does not claim they equal a tested max.