Enter a weight you've lifted and the reps you completed. Get your estimated 1RM from four validated formulas, plus an instant percentage chart showing the load for every training zone.
Your one-rep max (1RM) is the theoretical maximum weight you can lift for a single repetition with proper form. Knowing it lets you prescribe training loads by percentage — 85%+ for strength, 65–85% for hypertrophy, below 65% for muscular endurance. This free tool calculates your 1RM and builds the full percentage chart instantly. No account required.
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| % of 1RM | Weight (kg) | Approx reps (to failure) | Zone |
|---|
Rep approximations based on Prilepin's chart and NSCA guidelines. Actual reps to failure vary by individual, lift, and fatigue level.
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Your one-rep max (1RM) is the maximum load you can lift for a single complete repetition of an exercise with correct form. It is the foundational reference point for percentage-based strength programming. By expressing every training load as a percentage of your 1RM, you can precisely target specific neuromuscular adaptations — strength, hypertrophy, or muscular endurance — regardless of the absolute weight on the bar.
A true 1RM test requires significant neural activation, careful warm-up, and ideally a spotter. Testing too frequently accumulates fatigue and injury risk. Estimated 1RMs from submaximal sets (3–6 reps at near-failure) are sufficiently accurate for programming purposes and are safer to perform regularly. Most powerlifters formally test 1RM only at competitions or at the end of a training cycle.
Once you have an estimated 1RM, every training load becomes a fraction of that number. A 5×5 at 80% 1RM means the same relative effort for a 60 kg lifter as for a 200 kg lifter — the absolute weights differ but the physiological demand is equivalent. This makes percentage-based programming transferable, comparable, and scalable across all experience levels.
At 1–5 reps, all four formulas produce nearly identical results (within 1–2%). The divergence grows above 8 reps because the load-to-repetition relationship is not perfectly linear — slow-twitch fibre recruitment increases, fatigue curves differ between individuals, and rep quality degrades. For sets of 10+ reps, use the average of all four formulas and treat the result as a conservative estimate.
Many programs (5/3/1, Texas Method) prescribe percentages off a "training max" set at 90% of your estimated 1RM. This creates a conservative baseline that leaves room for daily variation in strength, reduces injury risk, and ensures you can always hit prescribed reps. When a cycle completes, you increase the training max by 2.5–5 kg and repeat — a sustainable linear progression.
Each formula was derived from different populations and validation methodologies. Understanding what each one measures helps you choose which result to weight most heavily for your training context.
| Formula | Equation | Best for | Rep range accuracy |
|---|---|---|---|
| Epley (1985) | w × (1 + r/30) | General use, most cited | 1–10 reps |
| Brzycki (1993) | w × (36 / (37 − r)) | Lower rep ranges, powerlifting | 1–8 reps |
| Lander (1985) | w / (1.013 − 0.0267123 × r) | Higher rep ranges | 5–12 reps |
| O'Conner (1989) | w × (1 + 0.025 × r) | Conservative estimate | 1–15 reps |
Where w = weight lifted, r = reps performed. Sources: Epley BF (1985); Brzycki M (1993); Lander J (1985); O'Conner B et al. (1989).
The percentage chart generated by this tool maps directly to three primary training zones. Each zone recruits different muscle fibre types, produces different hormonal and neural adaptations, and requires different recovery protocols.
Heavy loading in this zone maximises neural adaptations — motor unit synchronisation, rate coding, and intermuscular coordination. Myofibrillar hypertrophy (increasing contractile protein density) also occurs, but the primary adaptation is increased force production per motor unit. Strength zone training requires longer rest intervals (3–5 minutes) and higher intra-workout recovery. This is the domain of powerlifting and Olympic weightlifting protocols.
This range produces a high degree of metabolic stress and mechanical tension simultaneously — the two primary hypertrophy drivers identified in the literature (Schoenfeld, 2010). Moderate loads allow sufficient volume per set to accumulate total tonnage while staying close enough to failure to recruit high-threshold motor units. Rest intervals of 60–120 seconds increase metabolic stress; 2–3 minutes allow more volume per session. Most bodybuilding programs operate in this zone.
Low-load, high-rep training primarily develops slow-twitch fibre oxidative capacity and local muscular endurance. It is less effective for maximum strength or hypertrophy unless sets are taken very close to or to failure, in which case even 30% 1RM loads can produce significant hypertrophy (Morton et al., 2016). This zone is used for warm-up sets, deload weeks, rehabilitation, and athletes in endurance sports needing muscular durability rather than maximum strength.
Pick a recent set where you reached or came within 1–2 reps of failure. Sets of 3–6 reps are ideal. Avoid using warm-up sets or sets where you stopped well short of failure — the formulas require near-maximal effort to be accurate. If you have multiple qualifying sets, use the heaviest one.
Type the weight you lifted and the number of reps you completed. The calculator updates in real time. Switch between kg and lbs using the unit toggle — your inputs are converted automatically when you switch. The four formula results and their average appear immediately.
Scroll down to the generated table. Each row shows the weight you should lift at that percentage of your estimated 1RM, along with an approximate rep range to failure. Use this to plan your next session: if your program calls for 4×6 at 80%, find the 80% row and load that weight on the bar.
Your 1RM changes as you get stronger. Re-run this calculator after each training cycle using your latest working-weight performance. Percentage-based programs rely on accurate 1RM data — an underestimated 1RM results in training too light; an overestimated one produces sets you can't complete. For automated 1RM tracking across every lift and session, use the Personal Trainer app, which calculates estimated 1RM from each logged set.
If you stopped at 8 reps when you had 4 more in the tank, the formula will drastically underestimate your 1RM. Always use sets taken to or within 1–2 reps of true failure. This is called reps-in-reserve (RIR) — aim for RIR 0–2 when measuring for 1RM estimation.
Above 10 reps, formula accuracy drops significantly. A set of 20 reps to failure will produce 1RM estimates that are 10–20% off. Use a heavier weight for fewer reps whenever you plan to estimate your 1RM for programming purposes.
The estimate assumes all effort was identical and form was consistent. Fatigue from a long session, poor warm-up, or high psychological arousal can shift the estimate ±5%. Treat the output as a planning number, not a definitive maximum. If programming prescribes 95%+ loads, test your actual 1RM first.
A 1RM estimate from 6 months ago is stale. Strength adapts quickly — most intermediate lifters gain 5–15% on major lifts over a 12-week block. Using old percentages means training at incorrect intensities. Re-estimate at the start of each new training block, or whenever your top-set performance changes significantly.
No single formula is universally best. Epley and Brzycki are most accurate for 1–8 reps; Lander and O'Conner perform better above 8 reps. The average of all four is the safest estimate for programming. For maximum accuracy, formally test your actual 1RM every 8–12 weeks in a fresh session with a spotter.
Yes — the formulas are lift-agnostic. They work for squat, bench, deadlift, overhead press, weighted pull-ups, and most compound movements. They are less reliable for isolation exercises (curls, lateral raises) because form breakdown under fatigue makes the true rep ceiling unpredictable.
Yes. Your last inputs (weight, reps, unit) are saved in your browser's localStorage. They persist across page reloads and browser restarts. Nothing is sent to a server. Use the Reset button to clear the stored values.
A training max is 90% of your estimated 1RM. Programs like Jim Wendler's 5/3/1 prescribe all working percentages off the training max rather than the true 1RM. This builds in a fatigue buffer and means you can always complete the prescribed sets even on a suboptimal day. If a program says to use a training max, multiply your estimated 1RM by 0.9 and use that as your baseline.
Re-estimate at the start of each new training block (typically every 4–8 weeks). Novice lifters should re-estimate more frequently — strength gains are rapid early and old estimates become stale within 2–3 weeks. Intermediate and advanced lifters can re-estimate every 4–6 weeks. Any time your top-set performance shows a clear improvement, update the estimate.
Personal Trainer estimates your 1RM from every logged set, suggests percentage-based loads for the next session, and tracks your strength over time — all offline, one-time purchase.