Free tool
One-Rep Max Calculator
Estimate the most you could lift for a single rep from a set you've already done, then read the training percentages off it. How it works is explained right under the calculator.
| Training focus | % of 1RM | Load |
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How the estimate works
This calculator uses the Epley equation, a widely used way to estimate a one-rep max from a submaximal set: 1RM ≈ weight × (1 + reps ÷ 30). Lift 225 for 5 reps and it estimates a max near 262. The math is simple, but the accuracy depends entirely on the set you feed it: a set taken close to failure at a moderate rep range (about 3–8 reps) gives the most reliable estimate. Very high-rep sets drift because endurance, not maximal strength, starts to dominate.
If you left reps in reserve, this tool adds them back before estimating, so a hard set of 5 with "2 left" is treated as an effective 7-rep effort. That keeps the estimate honest instead of overstating a max from a set you could have extended.
What the percentages are for
Once you have an estimated max, training loads are usually written as a percentage of it. Heavier percentages train maximal strength and neural drive; moderate percentages build muscle through accumulated volume; lighter percentages move fast to train power and bar speed. Traditional strength, hypertrophy, powerbuilding, and conjugate-style plans can all use these ranges (either emphasizing one quality or combining them across the week) so you can keep progressing without making every session a maximal test.
Percentages are a starting point, not a law. Day-to-day readiness moves your real capacity around, which is why autoregulating with reps-in-reserve or RPE on top of percentages produces better long-run results than chasing fixed numbers. RPE and RIR explain how that autoregulation works.
Where this fits for lifters who run
If you also run, your true strength on any given day is affected by how much running load you are carrying. A heavy squat session the day after a long run rarely goes the way the spreadsheet promised. Mass in Motion tracks lifting and running load together and adjusts prescribed loads when your recovery says to, so the percentages you train at reflect what your body can actually handle that week, not just what a calculator said in the abstract. Learn more about hybrid athlete training and managing training load.