1RM Calculator (Lander Formula)
Knowing your one-rep maximum (1RM) is essential for programming strength and hypertrophy training because it allows you to set precise training loads as percentages of your maximum. Performing a true 1RM test is risky and fatiguing, so prediction formulas let you estimate it from a sub-maximal set. The Lander formula was developed by John Lander in 1985 and is one of the most validated 1RM prediction equations in the literature. It is most accurate for sets of 1 to 10 repetitions. Enter the weight you lifted and the number of reps you completed (stopping before failure is fine, but reps to or near failure give the most accurate estimate), and this calculator returns your predicted 1RM along with the standard training percentages from 50% to 95% so you can immediately apply the result to your programming.
Lander 1RM formula
1RM = (100 x Weight) / (101.3 - 2.67123 x Reps)
Where Weight is the load lifted and Reps is the number of repetitions completed. Most accurate for 1 to 10 reps.
Training load percentages
- 50 to 65%: Muscular endurance (15 or more reps)
- 67 to 85%: Hypertrophy (6 to 12 reps)
- 85 to 95%: Strength (1 to 5 reps)
- 95 to 100%: Maximal strength and peaking
Frequently asked questions
What is a one-rep max (1RM)?
A one-rep max is the maximum load you can lift for a single repetition with proper form. It is the gold standard measure of maximal strength and is used to set training loads as percentages of 1RM.
What is the Lander formula?
The Lander formula (1985) estimates 1RM as: 1RM = (100 x weight) / (101.3 - 2.67123 x reps). It was developed by John Lander and is considered highly accurate for sets of 1 to 10 repetitions, with accuracy declining for higher rep sets.
How accurate are 1RM prediction formulas?
1RM prediction formulas are most accurate when the test set uses 1 to 6 repetitions. At higher rep ranges (10 or more), accuracy can deviate by 5 to 15%. A direct 1RM test is always the most accurate method, but it carries higher injury risk.
What percentages of 1RM should I train at?
General NSCA guidelines: 55 to 65% for muscular endurance, 67 to 85% for hypertrophy, 85 to 100% for maximal strength. Power development typically uses 30 to 70% with high velocity intent.
Can I use this for any exercise?
Yes, the Lander formula can be applied to any exercise. However, 1RM estimates are most reliable for exercises with well-defined technique such as squat, bench press, and deadlift. For isolation exercises and machines, results are less reliable.
Official sources
- National Strength and Conditioning Association: NSCA Training Load Guidelines.
- American College of Sports Medicine: ACSM Resistance Training Position Stand.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.