STARK / Tools
1RM calculator: estimate your one-rep max
Enter a weight and the number of clean reps you managed. You get your estimated 1RM and the loads to use for each training goal.
Calculate your 1RM
Estimated 1RM
– kg
Your training loads
| % of 1RM | Load | Typical reps | Goal |
|---|
Short answer: 1RM ≈ weight × (1 + reps ÷ 30). For 80 kg × 5 reps, that gives about 93 kg. The estimate is most reliable between 2 and 10 reps.
How is your 1RM calculated?
The calculator averages three classic formulas. Each one models how many reps you can do at a given percentage of your max.
| Formula | Equation | Best for |
|---|---|---|
| Epley | w × (1 + r / 30) | Sets of 3 to 10 reps |
| Brzycki | w × 36 / (37 − r) | Low reps, slightly more conservative |
| Lombardi | w × r0.10 | Smooths results at higher reps |
w is the weight lifted and r the number of reps completed with good form. With a single rep, your 1RM is simply the weight lifted.
Which percentage for which goal?
- Strength: 85 to 95 % of 1RM, 1 to 5 reps, long rests (2 to 5 min).
- Muscle growth: 65 to 85 % of 1RM, 6 to 12 reps, close to failure.
- Muscular endurance: 50 to 65 % of 1RM, 15 reps or more, short rests.
These ranges are starting points. The best guide stays your own log: if every set feels easy, add weight; if your reps drop session after session, lighten the load or rest more.
How accurate is the estimate?
- Most reliable between 2 and 10 reps; beyond 10, treat the result as a rough guide.
- Count only clean reps, with the full range of motion.
- Built for compound lifts (squat, bench press, deadlift, overhead press). Machines and isolation moves vary more.
- Fatigue matters: a set at the end of a session underestimates your max.
Track your 1RM without doing the maths
STARK estimates your 1RM from every set you log, shows which lifts are progressing and suggests your next loads. Free on iPhone, with Apple Watch.
Frequently asked questions
What is a 1RM?
Your 1RM (one-rep max) is the heaviest load you can lift for a single clean repetition on a given exercise. It is the usual reference for setting training loads as a percentage.
Which 1RM formula is the most accurate?
No formula is exact for everyone. Epley and Brzycki give very close results between 2 and 10 reps; averaging several formulas smooths out their differences, which is what this calculator does.
Should I test my real 1RM?
Not necessarily. An estimate from a hard set of 3 to 8 reps is enough to plan your loads, and it is far less risky than a true max attempt. If you do test it, warm up progressively and use a spotter or safety bars.
Why do my estimates differ between exercises?
Formulas were built mostly from compound lifts such as the bench press and squat. On isolation or machine exercises, and on very high-rep sets, the estimate is less reliable.
How do I track my 1RM over time?
Log your sets with the weight and reps you actually did. STARK estimates your 1RM from those sets and shows which exercises are progressing the most.