Which formulas does this calculator use?

It runs seven established 1RM models — Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner and Wathan — and reports the average as your headline estimate, plus the full range so you can see how much the models disagree. Each formula is a regression fitted to real lifting data, so averaging several reduces the bias of relying on any single one.

Why do the formulas give different numbers?

Each model was fitted to a different data set of lifters and exercises, so they extrapolate differently. Epley and O'Conner are linear and read slightly higher at high reps; Brzycki is linear but breaks down as reps approach 37; Mayhew and Wathan are exponential and tend to sit in the middle. The spread shown next to your estimate tells you how confident you can be.

What are the training percentages for?

Strength and hypertrophy programmes prescribe work as a percentage of your 1RM — for example 5 reps at 87 percent or 10 reps at 75 percent. The table converts your estimated max into target weights in both kg and lb for common rep ranges, and labels each row as strength, hypertrophy or endurance work.

What is the 5/3/1 training max?

Jim Wendler's 5/3/1 programme bases working sets on a training max equal to about 90 percent of your true one-rep max, not the max itself. Building progress on a slightly conservative number leaves room to keep adding weight for longer and reduces missed lifts, so the calculator shows that 90 percent figure directly.

How accurate is the estimate at high reps?

It is most accurate for sets of about 10 reps or fewer. Beyond 10 to 12 reps, fatigue, breathing and technique introduce error, and the Brzycki model in particular becomes unreliable as reps climb toward 37. The tool caps input at 30 reps and flags that higher-rep estimates carry more uncertainty.

Is my lift data uploaded anywhere?

No. Every calculation runs entirely in your browser using JavaScript, and your last inputs are saved only in your own browser's local storage. Nothing is sent to a server, so your training numbers stay private.

One Rep Max Calculator (Pro)

Your one-rep max (1RM) is the heaviest weight you can lift for a single clean repetition. It is the reference point most strength programmes are built around — but actually testing it is risky, tiring and needs a spotter. This advanced calculator estimates your 1RM from a set you have already completed, then turns that number into everything you need to program your next training block.

Enter the weight and reps from a recent working set, pick kilograms or pounds, and the tool runs seven of the most widely used 1RM estimation formulas at once. Instead of trusting a single model, it averages them for a robust headline figure and shows you the full range so you can judge how much the formulas agree. You also get a comparison chart, a complete training-percentage table in both kg and lb, a 5/3/1 training max, and a plate-loading breakdown for any standard barbell.

How it works

The calculator computes seven independent estimates and averages the valid ones:

Epley: 1RM = w × (1 + reps / 30)
Brzycki: 1RM = w × 36 / (37 − reps)
Lander: 1RM = 100 × w / (101.3 − 2.67123 × reps)
Lombardi: 1RM = w × reps^0.1
Mayhew: 1RM = 100 × w / (52.2 + 41.9 × e^(−0.055 × reps))
O’Conner: 1RM = w × (1 + reps / 40)
Wathan: 1RM = 100 × w / (48.8 + 53.8 × e^(−0.075 × reps))

Here w is the weight you lifted and reps is the number completed. Some formulas are only defined over a limited rep range, so the tool drops any that become mathematically unstable before averaging. Unit conversion uses the exact factor 1 lb = 0.45359237 kg, so the kg and lb columns always agree.

From the averaged max it then derives target weights at standard percentages (for example 87 percent for a 5-rep strength set and 75 percent for a 10-rep hypertrophy set), a 90 percent training max for percentage-based programmes, and the plates you would load on each side of the bar.

Worked example

Suppose you bench press 100 kg for 5 reps. The formulas estimate:

Epley: 100 × (1 + 5/30) = 116.7 kg
Brzycki: 100 × 36 / (37 − 5) = 112.5 kg
Lombardi: 100 × 5^0.1 = 117.5 kg
O’Conner: 100 × (1 + 5/40) = 112.5 kg

Averaged across all seven models the estimate lands at roughly 115 kg (about 254 lb), with a typical spread of only a few kilograms. Your 90 percent training max would be about 103 kg, and a 5-rep strength set at 87 percent would call for roughly 100 kg — exactly the weight you just used, confirming the estimate is sensible.

Reps	% of 1RM	Target (kg)	Target (lb)
1	100%	115	254
3	90%	104	229
5	87%	100	221
8	80%	92	203
10	75%	86	190
12	70%	81	178

A quick note on the formula: linear models like Epley assume each extra rep costs a fixed slice of your max, which works well up to about 10 reps but drifts at higher rep counts. Exponential models like Mayhew and Wathan curve more realistically at the extremes, which is exactly why averaging several of them gives a steadier number than any single equation.

Every figure is calculated in your browser; nothing is uploaded or stored on a server.