One Rep Max Calculator – Find Your 1RM Instantly
The one rep max calculator estimates the maximum weight you can lift for a single repetition of any exercise — your 1RM. Simply enter the weight you lifted and how many reps you completed, and the calculator applies proven scientific formulas to predict your true max. Knowing your 1RM is essential for programming strength training, setting goals, and tracking progress over time.
Enter the weight you lifted for the set (in pounds or kg).
Enter the number of repetitions you completed. Best accuracy between 2–10 reps.
Choose which 1RM estimation formula to use. Epley is the most widely used.
Your results will appear here
How to Use This Calculator
1. Enter the weight you lifted in the 'Weight Lifted' field (in pounds or kilograms — just be consistent). 2. Enter the number of reps you completed in 'Reps Performed'. For best accuracy, use a set where you performed between 2 and 10 reps near your maximum effort. 3. Select the estimation formula you'd like to use from the dropdown — Epley is the most widely used and generally accurate option. 4. Click Calculate to see your estimated 1RM and a full percentage-based training table showing weights for different intensity zones.
What Is a One Rep Max (1RM)?
Your one rep max (1RM) is the maximum amount of weight you can lift for a single complete repetition of a given exercise with proper form. It is the gold standard for measuring absolute strength and is used by powerlifters, athletes, and coaches worldwide to design training programs.
Why Calculate Your 1RM?
Directly testing your 1RM carries injury risk, especially for beginners. Estimating it from a sub-maximal set (e.g., 5–8 reps at a challenging weight) gives you a safe and reliable number to work from. Once you know your 1RM, you can:
- Calculate training loads at specific percentages (e.g., 75% for hypertrophy)
- Program progressive overload more precisely
- Compare your strength to normative standards
- Track strength gains over months and years
1RM Estimation Formulas
Several validated formulas exist to estimate 1RM from a sub-maximal effort. Here are the ones included in this calculator:
Epley Formula (Most Common)
1RM = Weight × (1 + Reps / 30)
Developed by Boyd Epley in 1985, this is the most widely cited formula and is built into many gym management systems. It tends to slightly overestimate at higher rep ranges.
Brzycki Formula
1RM = Weight × (36 / (37 − Reps))
Matt Brzycki's formula is popular among strength coaches and is considered more accurate for sets of 10 reps or fewer. It breaks down mathematically at 37 reps.
Lander Formula
1RM = (100 × Weight) / (101.3 − 2.67123 × Reps)
The Lander formula is research-backed and performs well across a moderate rep range.
Lombardi Formula
1RM = Weight × Reps^0.10
A simple power-based formula that tends to underestimate slightly compared to others.
Mayhew et al. Formula
1RM = (100 × Weight) / (52.2 + 41.9 × e^(−0.055 × Reps))
Derived from research on football players, this formula uses an exponential function and is well-validated for the bench press.
O'Conner et al. Formula
1RM = Weight × (1 + Reps / 40)
A conservative variation of the Epley formula that tends to produce slightly lower estimates.
Wathan Formula
1RM = (100 × Weight) / (48.8 + 53.8 × e^(−0.075 × Reps))
Another exponential formula validated across multiple exercises and subject populations.
Percentage-Based Training Table
Once your 1RM is known, you can use percentages to guide your training intensity. Common training zones include:
- 90–100% 1RM: Maximum strength, 1–3 reps per set
- 80–90% 1RM: Strength development, 3–5 reps per set
- 70–80% 1RM: Hypertrophy (muscle growth), 6–12 reps per set
- 60–70% 1RM: Muscular endurance, 12–20 reps per set
- Below 60% 1RM: Active recovery, warm-up, and technique work