ONE REP MAX CALCULATOR
Estimate your one-rep max from any set.
Estimated One-Rep Max
PERCENTAGE OF 1RM
Working weights at each percentage of your estimated 258 lb max, rounded to the nearest 5 lb for easy loading. The percentage column is shaded by intensity — lighter loads run green, heavier loads run red.
| % of 1RM | Weight | Approx. reps |
|---|---|---|
| 100% | 260 lb | 1 |
| 95% | 245 lb | 2 |
| 90% | 230 lb | 3–4 |
| 85% | 220 lb | 5–6 |
| 80% | 205 lb | 7–8 |
| 75% | 195 lb | 9–10 |
| 70% | 180 lb | 11–12 |
| 65% | 170 lb | 14–15 |
| 60% | 155 lb | ~18 |
| 55% | 140 lb | ~20 |
| 50% | 130 lb | ~24 |
What is a one-rep max?
Your one-rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise with good technique. It's the universal yardstick for strength, and nearly every structured strength program — from linear progression to 5/3/1 — sets your working weights as a percentage of it. Rather than risking a true max attempt, you can estimate your 1RM from a heavier set of a few reps, which is exactly what this calculator does.
How this calculator works
Enter the weight you lifted and the number of clean reps you completed. The calculator runs four proven 1RM formulas and averages them so the estimate isn't skewed by any single equation:
- Epley — weight × (1 + reps ÷ 30)
- Brzycki — weight × 36 ÷ (37 − reps)
- Lombardi — weight × reps^0.10
- O'Conner — weight × (1 + reps ÷ 40)
These formulas are most accurate in the 1–5 rep range and drift higher as reps increase, so for the tightest estimate, use a weight you can lift for 5 reps or fewer.
Turning your 1RM into a program
Once you know your max, the percentage table above becomes your loading guide: warm-ups in the 50–70% range, hypertrophy work around 67–80%, and heavy strength work at 85%+ . Many programs use a training max (about 90% of your true 1RM) to keep working weights sustainable. Doing this by hand every session gets tedious fast — Cornerstone Strength estimates your 1RM automatically from every set you log, tracks how it trends over time, and prescribes percentage-based working weights for you.
FREQUENTLY ASKED QUESTIONS
What is a one-rep max (1RM)?+
Your one-rep max is the heaviest weight you can lift for a single, full repetition of an exercise with good form. It's the standard benchmark for maximal strength and the foundation of percentage-based programming.
How accurate is an estimated one-rep max?+
Estimates from a heavy set of 1–5 reps are typically within a few percent of a true max. Accuracy drops as the rep count rises, so for the best estimate use a weight you can lift for 5 reps or fewer.
Which formula does this calculator use?+
It averages four well-established formulas — Epley, Brzycki, Lombardi, and O'Conner — so the estimate doesn't hinge on the quirks of any single equation.
How do I use my 1RM to program training?+
Most strength programs prescribe loads as a percentage of your 1RM (or a slightly reduced 'training max'). Use the percentage table to set warm-ups and working weights. Cornerstone Strength estimates your 1RM automatically from every set you log and applies those percentages for you.
How often should I test my one-rep max?+
Testing a true 1RM is fatiguing, so most lifters avoid doing it often. Instead, let your estimated 1RM update continuously from working sets and re-evaluate every 4–8 weeks.
STOP DOING THE MATH
Cornerstone Strength tracks your estimated 1RM from every set and builds percentage-based programs automatically. Log the lift — we'll handle the numbers.
