How to use this calculator
Enter the weight you lifted and how many reps you completed with it — ideally a set taken at or near failure with good form. Hit calculate and you will see your estimated one-rep max from three validated formulas, plus a full percentage chart you can program from.
What is a one-rep max?
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It is the standard benchmark for strength, and almost every serious training program — from 5/3/1 to Starting Strength to powerlifting peaking blocks — prescribes working weights as percentages of your 1RM.
Testing a true 1RM is taxing and carries injury risk, which is why estimating it from a submaximal set is often the smarter choice — especially for newer lifters.
How is 1RM estimated?
This calculator runs your set through three of the most widely used prediction equations and shows you each result plus the average. The formulas agree closely in the 2 to 10 rep range and diverge slightly at higher reps.
The three formulas
Epley: 1RM = w × (1 + r ÷ 30)
Brzycki: 1RM = w × 36 ÷ (37 − r)
Lander: 1RM = (100 × w) ÷ (101.3 − 2.67123 × r)
Formula sources: Epley B. Poundage Chart. Boyd Epley Workout, University of Nebraska, 1985. Brzycki M. Strength testing — predicting a one-rep max from reps-to-fatigue. JOPERD, 1993. Lander J. Maximum based on reps. NSCA Journal, 1985.
Example: 225 lbs × 5 reps
| Formula | Estimated 1RM |
|---|---|
| Epley | 262.5 lbs |
| Brzycki | 253.1 lbs |
| Lander | 255.8 lbs |
| Average | ~257 lbs |
Why use estimated 1RM instead of testing?
- Safer — no maximal attempt means far less injury risk, especially without a spotter
- Less fatiguing — a heavy set of 3 to 5 costs much less recovery than a true max attempt
- Testable weekly — you can track strength progress from normal working sets
- Accurate enough — within 2 to 5% of a true max for sets of 10 reps or fewer
Tips for an accurate estimate
- Use a set taken to failure or within 1 rep of failure — submaximal effort inflates nothing
- Keep reps at 10 or fewer — accuracy drops noticeably beyond that
- Use strict form — sloppy reps estimate a max you can't actually lift cleanly
- Estimate per lift — your squat, bench, and deadlift each need their own number
Frequently asked questions
For sets of 10 reps or fewer taken close to failure, 1RM formulas are typically accurate within 2 to 5% of a tested max. Accuracy is best in the 2 to 6 rep range and decreases as reps climb, because individual muscular endurance varies more at higher rep counts.
No single formula wins for everyone. Epley tends to estimate slightly higher at high reps, while Brzycki is slightly more conservative. That is why this calculator shows all three plus the average — the average is the most robust single number to program from.
A set of 3 to 6 reps taken at or near failure gives the most accurate estimate. Sets above 10 reps test muscular endurance as much as strength, and the formulas become noticeably less reliable.
Most coaches say no. Beginners' technique breaks down under maximal loads, raising injury risk, and their strength changes week to week anyway. Estimating from a 5-rep set gives a beginner everything they need to program safely.
Every 4 to 8 weeks, or whenever your working sets feel noticeably easier. Strength changes with training blocks, body weight, and sleep — programming from a stale max means lifting lighter than you should.
It depends on the goal: 85 to 95% for pure strength (1 to 5 reps), 70 to 85% for hypertrophy (6 to 12 reps), and 50 to 65% for endurance and speed work (15+ reps). The percentage chart above maps each zone to your own numbers.
Important
Not medical advice. Estimated maxes assume healthy joints and sound technique. Never attempt a true one-rep max without proper warm-up, safety equipment, and ideally a spotter. If you are new to barbell training, have a previous injury, or experience pain during lifts, consult a qualified coach or clinician first.