One Rep Max Calculator

What is 1RM and why calculate it?

1RM stands for one rep max — the heaviest weight you can move for a single, well-executed repetition of a lift. It is the universal currency of strength training: programs prescribe loads as percentages of 1RM, strength standards rank lifters by their 1RM relative to bodyweight, and meets are won and lost on it.

Most lifters never actually test a true 1RM. It is slow, it is risky if you train alone, and it taxes your recovery for days afterward. Instead, you estimate it from a heavy working set — say five reps at a weight that left one or two in the tank — using a 1RM formula. That estimate is good enough to drive your next training block.

How to use this 1RM calculator

1. Warm up properly. The weight you put into the calculator should come from a working set after a full warm-up, not a cold attempt.
2. Enter weight and reps. The reps box accepts 1–15. Above 10 reps, accuracy drops noticeably — the calculator will flag that.
3. Pick a formula. Epley is the default; it is the formula most strength coaches use as a back-of-napkin estimate. Brzycki is more conservative below 5 reps. Wathan handles higher reps best.
4. (Optional) add bodyweight and gender. The calculator will show your 1RM as a multiple of bodyweight and classify you as untrained, novice, intermediate, advanced or elite for the selected lift.
5. Read the percentage table. Use it to plan working weights for the rest of your training block.

A note on safety

Estimating a 1RM is safe — testing one is not. If you do decide to test, do it inside a power rack with safety pins set at the bottom of your range of motion, or with an experienced spotter. Never test a bench press 1RM alone with the bar unclipped. For most lifters, estimation from a heavy triple or five is enough; treat real 1RM attempts as an occasional benchmark, not a regular session.

The seven formulas

All popular 1RM formulas take the same two inputs (weight lifted and reps performed) and return an estimated 1RM. They differ in how they extrapolate from the rep range you trained in to a single. Here are the seven the calculator supports:

Epley       1RM = w × (1 + r / 30)
Brzycki     1RM = w × 36 / (37 - r)
Lander      1RM = (100 × w) / (101.3 - 2.67123 × r)
Lombardi    1RM = w × r^0.10
Mayhew      1RM = (100 × w) / (52.2 + 41.9 × e^(-0.055 × r))
O'Conner    1RM = w × (1 + r / 40)
Wathan      1RM = (100 × w) / (48.8 + 53.8 × e^(-0.075 × r))

For a single rep (r = 1), every formula collapses to 1RM = weight lifted. From 2–10 reps they agree to within a few percent. Above 10 reps, the linear formulas (Epley, O'Conner) start to over-estimate while the exponential ones (Mayhew, Wathan) hold up better.

Worked examples

• 225 lb × 5 reps bench press (Epley): 225 × (1 + 5/30) = 225 × 1.1667 ≈ 262.5 lb estimated 1RM. The percentage chart says 80% for sets of 8 lands at 210 lb.
• 140 kg × 3 reps deadlift (Brzycki): 140 × 36 / (37 - 3) = 5,040 / 34 ≈ 148.2 kg. A 90 kg lifter is at 1.65× bodyweight — intermediate territory.
• 60 kg × 10 reps squat (Wathan): (100 × 60) / (48.8 + 53.8 × e^(-0.75)) ≈ 79 kg. The same set in Epley gives 80 kg — under one kilo of disagreement.

Standard percentage chart

FAQ

What is 1RM?

One Rep Max — the maximum weight you can lift for a single repetition with good form. It is the standard benchmark for absolute strength and is used to set training percentages across most strength programs.

Which 1RM formula is the most accurate?

No single formula wins across all rep ranges. Epley and Brzycki are the most popular and give nearly identical answers from 2–10 reps. Wathan and Mayhew handle higher reps (12–15) more conservatively. For one source of truth, look at the average of all seven — that is what the comparison panel computes.

How often should I test my 1RM?

For most lifters, every 8–12 weeks is plenty. True 1RM testing is taxing and recovery-heavy. In between tests, estimate from your heaviest working sets using this calculator and adjust training loads from that.

Can I trust the estimated 1RM?

Estimates are most reliable in the 3–8 rep range and most accurate when reps are taken close to failure. Beyond 10 reps, accuracy drops noticeably — at 12+ reps the formulas can disagree by 10% or more. Treat any single-set estimate as a ballpark, not a hard number.

Why does the result say my reps may be inaccurate?

All 1RM formulas were derived from sets in the 2–10 rep range. Above 10 reps, your cardiovascular and muscular endurance start to matter more than absolute strength, so the math drifts. Use a heavier weight for fewer reps when you want a tighter estimate.

How do I actually use the percentage table?

For programs prescribing percentages of 1RM, look up the row that matches your day. For example, 5×5 strength work is usually programmed at 80–85% of 1RM. Hypertrophy work sits at 65–75% for sets of 8–12. Power singles and doubles live at 90–95%.

Should I really attempt my 1RM?

Only with a spotter or safety pins, and only after a full warm-up. Most lifters never need to test a true 1RM — an estimate from a heavy triple or five is enough to drive programming. If you are training alone, stick with estimates.

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Privacy

Every calculation runs in your browser. Your lifts, bodyweight and other inputs never leave your device — nothing is sent to a server, nothing is stored in cookies, nothing is logged. The only thing this site remembers is whether you prefer pounds or kilograms, kept locally so you do not have to toggle it every visit.