Estimating your one-rep max without testing a true max
Your one-rep max (1RM) is the most weight you can lift once with good form, and it is the reference point almost every strength programme is built around. Rather than repeatedly attempting a risky maximal single, you can estimate your 1RM from a normal working set — the weight you lifted and how many reps you managed. This calculator does exactly that, then turns the result into a ready-to-use percentage table for planning your training.
How the maths works
There is no single perfect equation, so this tool runs four respected formulas and reports
their average. With weight w and reps r:
- Epley:
1RM = w × (1 + r / 30) - Brzycki:
1RM = w × 36 / (37 − r) - Lombardi:
1RM = w × r^0.10 - Lander:
1RM = (100 × w) / (101.3 − 2.67123 × r)
All four agree almost exactly at a single rep and spread apart as reps climb, which is why averaging them gives a steadier estimate than relying on any one alone.
A worked example
Suppose you squat 100 kg for 5 reps. Each formula gives:
| Formula | Calculation | Estimated 1RM |
|---|---|---|
| Epley | 100 × (1 + 5/30) | 116.7 kg |
| Brzycki | 100 × 36 / (37 − 5) | 112.5 kg |
| Lombardi | 100 × 5^0.10 | 117.5 kg |
| Lander | (100 × 100) / (101.3 − 2.67123 × 5) | 113.7 kg |
The average is about 115 kg — your estimated one-rep max. From there, 80% (a common working load) is roughly 92 kg, and 90% is about 104 kg.
Reading the percentage table
Heavy: 90–100%
Singles, doubles and triples. Pure strength work — demanding, low volume, and best done fresh.
Moderate: 75–85%
The classic strength range of roughly 4–8 reps. Where most productive training volume lives.
Lighter: 50–70%
Higher-rep sets for technique, hypertrophy and conditioning, or for back-off and warm-up work.
Accuracy is best when the set you enter is close to failure and uses a low rep count. Above about 10 reps the estimate becomes a ballpark, because endurance varies far more between people than maximal strength does.