Free Online One Rep Max (1RM) Calculator
Estimate your one-rep maximum (1RM) — the heaviest weight you can lift for a single repetition — using 5 scientifically validated formulas including Epley and Brzycki. Our accurate free online one rep max calculator supports both US Imperial units and UK/EU Metric units, helping you plan strength loads safely within fitness guidelines recommended by the WHO, NHS, and CDC.
Your One Rep Max Results
Training Percentages
Based on your average 1RM. Use these weights to structure your training program.
| % of 1RM | Weight (kg / lbs) | Typical Reps | Purpose |
|---|
Free Online One Rep Max Calculator – Compute Your Max Lifting Strength
Your one-rep maximum (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 measurement of absolute strength in powerlifting, Olympic weightlifting, and strength training. Our accurate free online one rep max calculator lets you estimate this strength limit instantly, using either US Imperial units (pounds) or UK/EU Metric units (kilograms).
Testing your absolute 1RM carries a significant risk of muscle strain or injury. Public health bodies like the CDC, the NHS, and the WHO emphasize that resistance training is vital for bone density and muscle preservation as we age. Using submaximal training loads and calculating your estimated 1RM with Epley or Brzycki equations is a safer, CDC-aligned approach to progressive overload training.
- Set precise training loads based on percentages of your max
- Track strength progress objectively over time
- Follow periodized programs (e.g., 5/3/1, Conjugate Method)
- Compare your strength to population norms and set goals
Rather than testing your actual 1RM — which carries injury risk and requires a spotter — these formulas estimate your max from a submaximal set. Research shows that using 3–10 rep ranges gives the most accurate estimates. Sets over 10 reps tend to be less accurate because muscle endurance starts to influence performance.
Which 1RM Formula is Most Accurate?
There is no single universally "best" formula — accuracy depends on the rep range and the individual. Our calculator shows all five and averages them for the best overall estimate.
Brzycki (1993): 1RM = weight × 36 / (37 − reps)
Lombardi (1989): 1RM = weight × reps^0.1
Mayhew et al.: 1RM = (100 × weight) / (52.2 + 41.9 × e^(−0.055 × reps))
O'Conner et al.: 1RM = weight × (1 + 0.025 × reps)
Epley Formula
The most widely used formula, developed by Boyd Epley in 1985. Works well for 1–10 reps and is the basis for most gym-based 1RM estimation. Tends to slightly overestimate for very high rep ranges (15+).
Brzycki Formula
Developed by Matt Brzycki in 1993, this formula is most accurate for lower rep ranges (1–10 reps). It becomes mathematically undefined at 37 reps, so it's only used when reps ≤ 36. Many strength coaches prefer it for its accuracy in the 3–8 rep range.
Lombardi Formula
Uses a power function (reps^0.1) to model the relationship between reps and max strength. It tends to give higher estimates than other formulas at higher rep ranges and can be useful for tracking muscular endurance crossover.
Recommendation
For the most reliable estimate, use a weight you can lift for 3–8 reps with good form. The average of all five formulas, as shown in this calculator, provides the most robust estimate across different lifters and rep ranges.
Strength Standards by Bodyweight
Reference values (1RM as a multiple of bodyweight) for three common barbell lifts. Standards from strength research and competitive lifting databases.
| Exercise | Beginner | Intermediate | Advanced | Elite |
|---|---|---|---|---|
| Back Squat | 0.75× BW | 1.25× BW | 1.75× BW | 2.25× BW |
| Bench Press | 0.5× BW | 1.0× BW | 1.5× BW | 2.0× BW |
| Deadlift | 1.0× BW | 1.5× BW | 2.0× BW | 2.75× BW |
| Overhead Press | 0.35× BW | 0.65× BW | 1.0× BW | 1.3× BW |
| Barbell Row | 0.5× BW | 0.9× BW | 1.3× BW | 1.7× BW |
BW = Bodyweight. Standards are for adult males training consistently; female standards are approximately 80% of these values. Elite = competitive powerlifter/weightlifter level.
Frequently Asked Questions
How accurate is a submaximal one rep max calculator?
Submaximal 1RM calculations are highly accurate when using rep ranges between 3 and 8 repetitions. Within this window, equations like Epley and Brzycki yield results within 1% to 3% of a true clinical max. However, if you enter reps above 10, the accuracy drops because cardiovascular endurance and lactic acid tolerance begin to limit performance rather than absolute motor unit recruitment.
Can I use US Imperial units or UK/EU Metric units in this 1RM calculator?
Yes. Our free online one rep max calculator is unit-agnostic. Since the underlying mathematical coefficients (Epley's 30 or Brzycki's 36) calculate ratios, they work identically for US Imperial units (pounds/lbs) and UK/EU Metric units (kilograms/kg). Simply input your lifted weight in your preferred unit, and the output values and training percentage chart will match that standard.
What are the safety guidelines under CDC and NHS standards for testing 1RM?
The CDC and NHS standards recommend engaging in muscle-strengthening activities at least twice a week. However, when finding your lifting limits, both health agencies advise against lifting near-maximum loads without proper supervision, a spotter, or years of structural conditioning. Using a submaximal calculator is the recommended method to avoid skeletal or tendon injuries.
What percentage of 1RM should I lift for muscle growth (hypertrophy)?
According to modern sports science, the optimal intensity zone for muscle hypertrophy is between 70% and 80% of your 1RM, performing 8 to 12 repetitions per set. For absolute strength development, training loads are typically increased to 85% to 90% of your 1RM, targeting 1 to 5 repetitions, while power training often utilizes 50% to 60% with high concentric speed.