One-rep max calculator: estimate your 1RM

The one-rep max calculator estimates the heaviest weight you could lift for a single rep, using the weight and reps from a set you've already done — no need to actually attempt a risky true max. This 1RM calculator is useful for setting training percentages, tracking strength progress over time, and comparing effort across different rep ranges on the same lift.

How to use the calculator

Enter the weight you lifted and how many reps you completed with good form (up to 20), plus whether you're working in kilograms or pounds. The calculator returns an estimated 1RM along with a full percentage table showing roughly how much weight corresponds to different rep ranges, from a single heavy rep near 100% down to lighter, higher-rep sets around 50–60%. Use a set that was genuinely close to failure — a set with several reps left in the tank will underestimate your true max.

The Epley and Brzycki formulas, and their limits

This tool averages two well-established formulas. The Epley formula is weight × (1 + reps ÷ 30); the Brzycki formula is weight × 36 ÷ (37 − reps). Both estimate 1RM from a lighter, higher-rep set, and they tend to agree closely in the 1–10 rep range but diverge more at higher reps, which is why this calculator shows both individual estimates alongside the averaged result. Neither formula is exact — they're statistical estimates based on population data, not a measurement of your specific physiology, and accuracy drops noticeably above about 12–15 reps, since fatigue and technique breakdown start to matter more than raw strength at that point. Treat the result as a solid planning estimate, not a guaranteed number you'll hit on your first real attempt at that weight.

How to use your estimated 1RM in training

Most programs are built around percentages of your 1RM rather than the max itself: roughly 85%+ for low-rep strength work, 65–85% for muscle-building rep ranges, and below 65% for higher-rep endurance or technique work. The percentage table this tool generates lets you pick a working weight for any rep target without doing the math by hand each time. Recalculate every few weeks using your most recent hard set, since your 1RM changes as you get stronger — an outdated estimate will eventually have you training too light or too heavy for your current strength level.

Which lifts this works best for

The calculator works for any exercise with a clear weight and rep count, but is most reliable for the big compound barbell lifts — back squat, deadlift, barbell bench press and overhead press — where technique stays fairly consistent across a set. It's less reliable for exercises where form tends to break down or momentum creeps in at higher reps, like curls or lateral raises, since the formulas assume consistent technique throughout the set.

Turning your 1RM into a loaded bar

Once you have a target working weight from the percentage table, the plate calculator works out exactly which plates to load on each side of the bar. Together, the two tools take you from "here's a set I did" to "here's exactly what to load today," which removes the mental math of converting a percentage into a real barbell loadout on a busy gym floor.

Tracking strength over time

Logging your estimated 1RM after key sessions gives you a clearer trend line than watching your working weight alone, since it accounts for changes in both weight and reps together. A rep that used to be a real grind at a given weight, done for more reps than before, reflects genuine progress even if the top single-rep weight hasn't moved yet — the calculator surfaces that improvement numerically instead of leaving it to feel.

Safety note on testing a real max

Because this calculator exists precisely to avoid the risks of a true maximal attempt, use it as your primary way of tracking strength unless you have a specific reason (like competition prep) to test an actual 1RM with a spotter and proper warm-up protocol. If you do test a real max, warm up thoroughly with several increasing-weight sets first, and always use a spotter or safety pins on squats and bench press.

Privacy

All calculations run in your browser — the weight and reps you enter aren't sent anywhere or stored on a server, so there's nothing to sign up for and nothing saved unless you choose to keep a note of the result yourself.