Free tool
One rep max calculator
Enter a working set and we estimate your one rep max using the three formulas strength researchers actually use. Plus every training percentage from 60 to 100 percent, ready to load for your next session.
Estimated one rep max
93 kg
Epley
93kg
Brzycki
90kg
Lombardi
94kg
Training percentages
Common percentage targets from a working 1RM. Use these to load assistance work and pre-deload sessions.
What a one rep max actually tells you
Your one rep max is the heaviest weight you can lift once with technique that holds up. Every working set you ever do is a percentage of it. A 5x5 at 75 percent means something specific. A 3x3 at 90 percent means something else. Without a 1RM the language of strength training falls apart.
Most lifters do not want to actually test a 1RM. They should not. A true max attempt costs you a session. It risks an ugly rep on a stiff joint. It only really matters if you compete. Estimating the 1RM from a heavy submaximal set is safer and more useful, especially past 40 when recovery from a max attempt costs more than the data it produces.
The three formulas, and which to trust
The Epley formula is the strength-research default. Weight times one plus reps times 0.0333. It is accurate within a few percent for sets in the 1 to 10 rep range and tends to slightly overestimate on heavy fives.
The Brzycki formula uses weight divided by one minus reps times 0.0278. It performs slightly better on lower-rep sets (1 to 5) and slightly worse on higher reps. Powerlifters lean Brzycki.
The Lombardi formula is weight multiplied by reps to the power of 0.1. It runs hotter for higher-rep sets and is the closest match for sets of 8 to 10.
The headline 1RM on the calculator is the average of the three. The difference between them is rarely more than 5 percent.
How to use the training percentages
Below the headline figure are training percentages from 60 to 100. A rough rule. Strength work runs from 80 to 95 percent for sets of one to five. Hypertrophy lives at 65 to 80 percent for sets of six to twelve. Conditioning and assistance work sits below 65 percent at higher rep ranges. Deload weeks usually pull every working weight down to 60 to 70 percent of programme load.
Where this fits with the progressive overload calculator
This tool gives you the ceiling. The progressive overload calculator tells you what to do in the next session. The two work together. Estimate the 1RM, then plan the next jump.
Where STRNTH handles this automatically
Inside the STRNTH app every working set feeds a rolling 1RM estimate for each lift. The STRNTH Index reads the trend and tells you when your strength is climbing, plateaued or fatigued. Percentage-based assistance loads are pre-loaded on every working set in every programme. Browse the programmes to see how the numbers flow.