1RM Calculator
Calculate your estimated 1RM and see working weights by percentage
Methodology
- 1RM estimate (Epley etc.) — training guide only
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What does the 1RM calculator calculate?
The 1RM (One Rep Max) calculator is an online tool that estimates your maximum strength without performing an actual one-rep max test. The calculator shows your estimated 1RM based on weight and reps from your workouts, and displays working weights by percentage (50%, 60%, 70%, 80%, 90% of 1RM). The calculator uses proven formulas (Epley and Brzycki) to estimate your maximum strength. It's useful for anyone who wants to program their workouts based on percentages, track strength progress, or plan training without testing true 1RM (which can be risky). The calculator helps you make informed decisions about training loads and progression.
How to use the 1RM calculator?
The 1RM calculator helps you estimate your maximum strength without performing a one-rep max test. Enter the weight and reps from your last workout and the calculator will estimate your 1RM.
- Enter weight and reps: Enter the weight (kg) and number of reps from your last set.
- Select formula: Epley or Brzycki (formula names in the selector).
- Calculate: Click "Calculate" to see your estimated 1RM.
- Review working weights: See percentages of 1RM; both 1RM and table weights are rounded to whole kg.
Formulas:
- Epley: weight × (1 + reps / 30)
- Brzycki: weight × (36 / (37 − reps))
Example with specific numbers
Example: 100 kg × 5 reps (Epley)
- Weight: 100 kg
- Reps: 5
- Epley: 100 × (1 + 5/30) ≈ 116.67 → 117 kg (rounded to whole kg)
- Brzycki: 100 × (36 / (37 − 5)) = 112.5 → 113 kg
- Working weights from rounded Epley 1RM (117 kg), Math.round:
- 50% = 59 kg
- 70% = 82 kg
- 80% = 94 kg
- 90% = 105 kg
The two formulas give close but different estimates. Working percentages use the already rounded 1RM, matching the UI. Values are indicative.
Sources and notes
The calculator uses Epley (1985) and Brzycki (1993) formulas to estimate 1RM from submaximal loads. Estimates can differ from a true tested 1RM depending on exercise, form, fatigue, and other factors. Always prioritize safety and proper form.
Results are estimates from public formulas and general health guidance. Not medical advice — consult a professional for health decisions.
References:
- WHO — physical activity – General activity guidance
- WHO — healthy diet – General nutrition principles
- Mifflin–St Jeor (BMR/TDEE) – Common resting metabolic rate equation
- “How we calculate” – Formulas used on this page
Frequently Asked Questions
What is 1RM?
1RM (One Rep Max) is the maximum weight you can lift for one repetition with proper form.
Which formula should I use?
The selector offers Epley and Brzycki. Epley: weight × (1 + reps / 30). Brzycki: weight × (36 / (37 − reps)). Compare both if you want.
How accurate are the calculations?
The calculations are estimates. Your actual 1RM may vary depending on form, recovery, and other factors.