One Rep Max Calculator
Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Testing it directly is tiring and risky, so lifters estimate it from a lighter set taken close to failure: lift 100 kg for five good reps and a formula predicts your max. This calculator runs six well-known formulas — Epley, Brzycki, Lombardi, O’Conner, Mayhew and Wathan — averages them and shows the spread, then lists the weights for common training percentages. Use it to set working weights for strength programmes. It is an estimate: technique, fatigue and the exercise itself change how accurate the numbers are, and a true max attempt should only be made with a spotter and proper warm-up.
How to use the one rep max calculator
- Enter the weight you lifted and the number of clean reps you completed to (or near) failure.
- Choose kilograms or pounds.
- Read the average estimate and the range across formulas; the spread shows how uncertain the estimate is.
- Use the percentage table to choose working weights, for example 70–85% of 1RM for most strength and hypertrophy sets.
Formula
Epley: 1RM = w × (1 + reps ÷ 30). Brzycki: 1RM = w × 36 ÷ (37 − reps). Lombardi: 1RM = w × reps0.10. O’Conner: 1RM = w × (1 + 0.025 × reps). Mayhew and Wathan use exponential fits: 1RM = 100 × w ÷ (52.2 + 41.9 × e−0.055 × reps) and 100 × w ÷ (48.8 + 53.8 × e−0.075 × reps). The estimate shown is the average of the six. Formulas diverge more as reps increase and are least reliable above about 10–12 reps.
Worked examples
100 kg for 5 reps
The average estimate is 115.8 kg: Epley gives 116.7 kg, Brzycki 112.5 kg and Lombardi 117.5 kg — a range of 112.5–119 kg.
A heavy single
With 1 rep, the weight lifted is the max: 100 kg for 1 rep gives 100 kg on the Brzycki formula (others differ slightly because they add a small allowance).
In pounds
225 lb for 8 reps estimates a 1RM of about 280.5 lb.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- You squat 140 lb for 6 reps. What is your estimated 1RM?
Show answer
Estimated one-rep max (average of six formulas): 166.3 lb
Common mistakes to avoid
- Using a set with sloppy reps. The formulas assume each rep was completed with good form near failure.
- Using high-rep sets (15–30). Accuracy falls off quickly; use a heavier set of 3–8 reps.
- Comparing exercises. Estimates work differently for squats, deadlifts and bench presses.
- Attempting a true 1RM unprepared. Use a spotter, safety bars and a progressive warm-up.
- Treating the number as fixed. Your max changes with sleep, recovery and training.
Frequently asked questions
How do you calculate a one-rep max?
Use a formula such as Epley: weight × (1 + reps ÷ 30). This calculator runs six formulas and averages them.
Which 1RM formula is most accurate?
None is perfect. Brzycki and Epley are the most common; they agree closely at low reps and drift apart as reps rise. The average smooths this out.
How many reps should I use?
A set of 3–8 reps taken near failure gives the most reliable estimate.
What percentage of 1RM should I train at?
Strength work often uses 80–95% for low reps; muscle-building work often uses 65–85% for 6–12 reps. Follow a programme or coach.
Is it safe to test my true 1RM?
It carries injury risk. Do it only with a spotter, safety equipment, a good warm-up and, ideally, a coach.
Is this medical or coaching advice?
No. It is an educational estimate; consult a qualified coach or health professional.
Sources and further reading
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.