ToolNestFree One Rep Max (1RM) Calculator
Last updated: October 13, 2026
Quick answer: Testing a true one-rep max is risky — the smart way is to estimate it from a submaximal set. This free one rep max calculator takes the weight you lifted and the reps you managed and estimates your 1RM using six proven formulas (Epley, Brzycki, Lombardi, Mayhew, O'Conner, Wathan) plus an averaged consensus. It also converts both ways — find what weight to use for any rep target — and builds your full %1RM training table for programming strength, hypertrophy, and endurance work. Works in kg and lbs, entirely in your browser.
Estimates only — formulas are most reliable at 2–10 reps and for compound lifts. Always use a spotter and proper form; never attempt a true 1RM alone.
✓ Free forever · ✓ No signup · ✓ Tool inputs stay in your browser — never sent to our servers.
How to Use the One Rep Max Calculator
- Enter the weight you lifted and your unit (lbs or kg).
- Enter the reps you completed with good form — 2 to 10 reps gives the most reliable estimate.
- Pick a formula or leave the consensus average selected for the most robust number.
- Set a target rep count to convert — e.g. 'what weight should I use for sets of 8?'
- Read your estimated 1RM, the per-formula breakdown, and your full %1RM training table.
Why Use Our One Rep Max Calculator?
- Six proven formulas — Epley, Brzycki, Lombardi, Mayhew et al., O'Conner et al., and Wathan, not just one hidden equation.
- Consensus average — averages all six formulas to smooth out any single formula's bias.
- Bidirectional converter — 1RM from your set, then back: the right working weight for any rep target.
- Full %1RM training table — 100% down to 60% with the training goal each zone serves.
- kg and lbs — toggle units without re-entering anything.
- Honest validity warnings — flags when your rep count is outside the range where the formulas hold up.
Common Use Cases
- Programming a strength block: Turn last cycle's working sets into this cycle's percentages: one 5-rep set becomes a full 12-week %1RM plan.
- Picking working weights: 'What should my sets of 8 be?' — convert your known 5RM down to any rep target without mental math.
- Comparing formulas: See how Epley vs Brzycki vs Wathan differ on your numbers before trusting one blindly.
- Tracking progress: Re-test the same rep range monthly; a rising estimated 1RM is objective proof the program works.
- Coaching clients: Give athletes their %1RM table from a single submaximal test — no risky max-out sessions needed.
One Rep Max Calculator vs Alternatives
- easycalculation.com 1RM calculator: Shows several formulas but wraps them in heavy ads and dated pages. This page gives you the same multi-formula view plus the reverse converter and %1RM table, without the clutter.
- fitliferegime.com calculators: Decent single-formula tools (Brzycki, RPE-to-%1RM) spread across multiple pages. Here all six formulas, the consensus, and the training table live on one page.
- Doing the Epley formula by hand: w × (1 + r/30) is easy for one number — but you lose the other five formulas, the consensus, and the full % table. Fine for a quick check, slow for programming.
- Strength-tracking apps: Great for logging workouts over time; overkill if you just need this week's percentages. No install, no account, no subscription here.
If you log every workout, keep your app. For a fast, honest 1RM estimate with the full formula breakdown and a ready-to-use %1RM table, this page is the shorter path.
Frequently Asked Questions
How do you calculate one rep max?
The classic method: 1RM = weight × (1 + reps ÷ 30) (the Epley formula). Example: 225 lbs × 5 reps → 225 × (1 + 5/30) ≈ 263 lbs. Other respected formulas (Brzycki, Lombardi, Wathan…) give slightly different answers, which is why this calculator shows all six plus their average — the consensus.
What is the most accurate 1RM formula?
No single formula wins everywhere — accuracy depends on the lift, the rep range, and the lifter. Brzycki is the strength-coach favorite for low reps; Epley is the most widely cited; Wathan and Mayhew fit some lifters better at higher reps. Averaging several (the consensus option above) is the most defensible single number.
How many reps should I use to estimate my 1RM?
2–10 reps is the reliable range; 3–6 is the sweet spot. Above 10 reps the formulas drift — a 20-rep set measures endurance more than maximal strength, so estimates from it run high. The calculator warns you when the rep count leaves the trustworthy zone.
How do I convert my 5RM to an 8RM?
Estimate your 1RM from the 5-rep set, then work back down: weight = 1RM ÷ (1 + target reps ÷ 30). Example: a 263 lb 1RM → 8-rep working weight ≈ 263 ÷ 1.267 ≈ 208 lbs. Enter your target reps above and the converter does it instantly.
What percentages of 1RM should I train at?
Rough guide: 90–100% maximal strength (1–3 reps), 80–90% strength (3–6), 65–80% hypertrophy (6–12), 50–65% endurance (12+). Most programs live at percentages of 1RM rather than fixed weights — the training table above gives you every zone from your estimate.
Is a 1RM calculator accurate?
Within a few percent for most lifters on compound lifts in the 2–10 rep range — good enough for programming. It's an estimate, not a measurement: leverages, fatigue, and technique shift real maxes. Treat it as a planning number and validate with a conservative test when a program calls for a true max.
Should I test my real 1RM instead?
Only with a spotter, after a proper warm-up, and when your program actually needs it. For most training blocks, an estimated 1RM is safer and sufficient — many coaches never have athletes test true maxes. Use the estimate for percentages and re-test your working sets every few months.