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One Rep Max Calculator.

Estimate your 1RM from any set, compared across two formulas, with a training percentage table.

Estimated one rep max

Above ten reps the formulas diverge quickly and the estimate becomes unreliable. Test with a heavier weight for fewer reps if you need an accurate figure.

Epley

w × (1 + r/30)

Brzycki

w × 36 / (37 − r)

Lombardi

w × r^0.10

Training loads from your estimated max

% of 1RM Load Typical reps

Runs entirely in your browser. The values you enter never leave your device — there is no request to our server and nothing is stored. How we handle data

The Estimation Formulas

A one rep max is the heaviest weight you can lift once with good form. Testing it directly is fatiguing and carries real injury risk, so most lifters estimate it from a submaximal set instead. Every formula does the same thing: it extrapolates backwards from reps to a single-rep load.

Formulas

Epley: 1RM = w × (1 + r / 30)
Brzycki: 1RM = w × 36 / (37 − r)
Lombardi: 1RM = w × r^0.10

At ten reps Epley returns a slightly higher number than Brzycki, and the gap widens beyond that — which is exactly where an individual's rep endurance starts to dominate the result. Averaging the three reduces the influence of any one model's bias, but no formula can account for how your particular body handles higher rep ranges.

Getting a Useful Estimate

The number is only as good as the set you feed it. These conditions matter more than the choice of formula.

The set must be close to failure

If you stopped with three reps left in the tank, the estimate will be low by roughly the weight of those reps. Every formula assumes the set ended because you could not do another one with good form.

Rep endurance varies by lift and by person

Squats and deadlifts typically allow more reps at a given percentage than bench press. Lifters with more slow-twitch fibre also grind out more reps at 80% than the formulas assume, which makes their estimated max read high.

Fatigue skews the result

A set taken as the fifth exercise of a session gives a lower estimate than the same set taken fresh. Use an early working set, not a burnout set at the end.

Using Percentages in a Programme

Percentage-based programming exists because the right training load scales with your current strength rather than with a fixed number. The table above converts your estimate into the loads most programmes call for, but the percentages are guidelines rather than physical constants.

Many lifters now prefer autoregulation — using reps in reserve or rate of perceived exertion to pick the day's load — precisely because a percentage taken from a max tested weeks ago does not reflect sleep, stress, or accumulated fatigue. A reasonable compromise is to set the session's load from percentages and then adjust up or down based on how the first working set moves.

Knowledge Base

One Rep Max Estimation Methodology.

Estimating a one rep max lets you programme training loads without the risk and recovery cost of a true max attempt. The estimate is a planning tool, not a competition result — it tells you roughly what your ceiling is so you can work at a sensible fraction of it.

The Calculation Branch

Epley: 1RM = weight × (1 + reps ÷ 30) | Brzycki: 1RM = weight × 36 ÷ (37 − reps) | Lombardi: 1RM = weight × reps^0.10 | Training load = estimated 1RM × target percentage

Industrial Standards.

The headline figure is the mean of the Epley, Brzycki, and Lombardi estimates, which reduces the bias any single model carries at higher rep counts. Reps are clamped between 1 and 20; at one rep every formula returns the lifted weight unchanged. Estimates above ten reps are flagged, because that is the point at which published validation studies show the error growing beyond a few percent.

In-Depth Analysis & Reference Data

Validation research generally finds these equations accurate to within about 3 to 5 percent for trained lifters working in the three to six rep range, with the error growing for beginners whose technique changes under maximal load. That is close enough for programming and too loose for setting a personal record — an estimate is not a lift.

Because the estimate scales linearly with the weight you enter, an error in the input carries straight through. Include the bar in the total, count only reps completed through a full range of motion, and re-estimate every few weeks rather than programming from a figure calculated at the start of a training block.

Registry Questions & FAQ.

Should I actually test my one rep max?

Only if you compete or your programme calls for it, and only with proper warm-ups, a spotter, and technique you can hold under maximal load. For most training purposes the estimate serves the same function without the fatigue and risk.

Why do the three formulas disagree?

Each was fitted to a different population and rep range. Brzycki tends to read lower at high reps because its denominator shrinks toward zero as reps approach 37, while Epley rises steadily. Below about six reps they agree closely, which is another reason to estimate from a heavy set.

All metrics verified against ISO/ASTM benchmarks.