One Rep Max Calculator

1. Choose kilograms or pounds.
2. Enter the weight you lifted and the number of reps you completed with good form.
3. Read the estimated one-rep max, a second estimate and a suggested five-rep weight, all updating live.

Each result serves a purpose:

A one-rep max is the heaviest weight you can lift for a single, full repetition of an exercise with good form. It is the standard measure of maximal strength, used to compare lifters, track progress and set training loads as a percentage of the maximum. A squat programme might call for sets at 80 percent of your 1RM, for example.

Testing a true one-rep max is demanding and carries injury risk, so most lifters estimate it instead. By lifting a submaximal weight for several reps and applying a formula, you get a close prediction without the danger of a genuine maximal attempt.

It applies two well-known formulas that relate the weight and reps of a submaximal set to a one-rep maximum.

The Epley formula adds roughly one thirtieth of the weight for each rep beyond the first, while Brzycki uses a ratio that falls as reps rise. Both agree closely at low reps and drift apart as the set gets longer, which is why the estimate is most reliable for sets of about ten reps or fewer.

1. Take a weight you can lift for several clean reps.
2. Apply the Epley and Brzycki formulas to the weight and reps.
3. Read the estimated maximum and set training loads from it.

The five-rep suggestion is about 87 percent of the estimated maximum, a common working-set intensity.

Lift 100 for 5 reps. The Epley estimate is 100 x (1 + 5/30) = 116.7, and Brzycki gives 100 x 36 / (37 - 5) = 112.5. The two bracket a likely one-rep max of roughly 113 to 117.

To train at 80 percent of that maximum, you would use about 93 to 94. A five-rep working weight of about 87 percent comes out near 102, just above the weight you tested with.

Push the same 60 for 10 reps and the estimate rises to about 80, though longer sets like this make the prediction less precise than a heavier, lower-rep set.

Many programmes set loads as a share of your one-rep max; these are typical guides.

These pair a percentage with a rep range, so your estimated maximum turns directly into working weights for each goal.

The prediction is only as good as the set you base it on, and several things affect it.

Reps in the Set

Lower-rep sets give a more reliable estimate; long sets to failure introduce more error.

The Exercise

Formulas were derived mainly from big lifts like the squat and bench; they suit those better than isolation moves.

Form and Fatigue

Sloppy reps or a tired lifter inflate the rep count and overstate the maximum.

Experience

Trained lifters often match the formulas well, while beginners can vary more from the predictions.

Setting Training Loads

Turn an estimated maximum into working weights at 70, 80 or 90 percent for your programme.

Tracking Progress

Re-test with the same submaximal set over time to see your estimated maximum climb.

Avoiding Max Attempts

Get a strength benchmark without the risk of a true single-rep maximal lift.

1. Using Very High Reps

Sets beyond about ten reps make the estimate unreliable. Use a heavier, lower-rep set.

2. Counting Sloppy Reps

Only full reps with good form should count, or the maximum is overstated.

3. Treating the Estimate as Exact

It is a prediction. Two formulas give slightly different numbers for a reason.

4. Skipping the Warm-up

Test on a properly warmed-up set, and never chase a true max without preparation and a spotter.

5. Applying It to Any Exercise

The formulas suit compound lifts best and are less accurate for small isolation movements.

The formulas are good estimates for compound lifts at moderate reps, not exact measurements.

Lift a weight for several clean reps, then apply a formula. The Epley formula is weight x (1 + reps/30). For 100 lifted 5 times, that is about 117.

It is the most weight you can lift for a single full repetition of an exercise, the standard measure of maximal strength used to set training loads.

Epley and Brzycki are both widely used and agree closely at low reps. Neither is perfect; using both to bracket a range is a sensible approach.

Use a set of about ten reps or fewer. Heavier, lower-rep sets give a more reliable estimate than long sets taken to failure.

No. That is the point of the estimate. A submaximal set with a formula predicts your maximum without the risk of a true single-rep attempt.

Set working weights as a percentage of it: around 80 percent for strength at five reps, or 70 percent for muscle growth at eight to ten reps.

Epley and Brzycki use different equations, so they diverge as reps rise. At low reps they are very close; at high reps the gap widens.

Estimating from a submaximal set is far safer than a true max attempt. Still warm up well, keep good form and stop if anything hurts.

No. The calculation runs in your browser, and nothing you enter is sent anywhere unless you Save a result, which stays on this device only.

• One-repetition maximum (Wikipedia).
• Basal metabolic rate (Wikipedia).
• Protein and muscle (Harvard T.H. Chan School of Public Health).