One Rep Max Calculator

This one rep max calculator estimates the heaviest weight you could lift once, from a weight you can already lift for a known number of reps. Lifting 100 kg for 5 reps gives an estimated 1RM of 116.7 kg on the Epley formula, and the tables underneath convert that into a training weight for every rep count and every percentage. Use a set you can complete between 1 and 10 times, because the closer the test set is to a single rep, the closer the estimate lands.

What a one rep max is

A one rep max, written 1RM, is the most weight you can move for one complete repetition of an exercise with proper form. It is the number weightlifting competitions are decided on, because it represents the peak force your muscles can produce in a single all-out effort.

It is specific to the exercise, and that point gets missed constantly. Your bench press 1RM tells you very little about your squat, your deadlift, or your overhead press. Different lifts recruit different muscles across different ranges of motion and leverages, so each one needs its own number. Most people can deadlift far more than they bench, and the ratio between the two varies enormously from lifter to lifter depending on limb length, training history, and which muscles they have prioritised.

It is also not fixed. A 1RM measured in March is a historical fact about March. Strength moves with training, sleep, nutrition, stress, and time away from the gym, which is exactly why the number is worth re-measuring rather than treating as a permanent label.

Why it is worth knowing

The practical value is that it turns training intensity into arithmetic. Nearly every strength programme written in the last fifty years prescribes work as a percentage of 1RM: five sets of three at 85%, or three sets of ten at 70%. Without a 1RM, those instructions are unusable, and you are left guessing at weights, which usually means training too light on hard days and too heavy on easy ones.

It also gives you a single number to track. Strength gains are slow enough that they are hard to feel week to week, and a bodyweight that barely moves tells you nothing about what is happening underneath. Watching an estimated 1RM climb from 100 kg to 116 kg over a training block is concrete evidence that the programme is working. When it stops climbing, that is information too, and usually the signal to change something rather than to push harder.

Two ways to find it

You can measure a 1RM directly by working up to a single heavy lift, or estimate it from a lighter set using a formula. Both are legitimate. They differ in accuracy, in time, and in risk.

Testing it directly

A direct test means progressively adding weight, resting between attempts, until you reach a load you can lift exactly once with clean technique. The protocol matters:

• Warm up thoroughly. Raise the temperature of the muscles you are about to load, then do several progressively heavier warm-up sets of the lift itself. Cold maximal attempts are how people get hurt.
• Get a spotter. On a bench press this is not optional. A spotter also gives you an outside opinion on whether a rep was genuinely clean.
• Start at a weight you could manage for five to ten reps. Too light wastes energy across too many attempts; too heavy risks a failed lift before you are properly warm.
• Rest fully between attempts. Two to five minutes, and toward the top end as the weight climbs. Cutting rest short is the most common reason a test underestimates the real number.
• Add weight in shrinking increments. Big jumps early, small ones as the weight approaches your limit. How the last set felt tells you how much to add next.
• Stop when form breaks. A rep completed with a bounced bar, a rounded back, or a spotter's fingers on it is not a rep. Compromised form gives you a higher number and an injury risk, which is a bad trade in both directions.

The advantages are simplicity and accuracy: keep adding weight until only one rep is possible, and you have measured the thing itself rather than modelled it. The disadvantages are the injury risk that comes with deliberately approaching failure under heavy load, and the time, since a full test with proper rest can take the better part of an hour.

Beginners are usually better served by estimation. In the first months of training, the priority is learning technique under manageable loads, and a maximal attempt with unpractised form is a poor use of the risk budget. That said, a beginner still benefits from knowing roughly where their max sits, which is what the formulas are for.

Estimating it from a set

This calculator offers the three most widely used equations. Each takes the weight you lifted and the reps you completed:

Epley: 1RM = weight × (1 + reps ÷ 30)

Brzycki: 1RM = weight × 36 ÷ (37 − reps)

Lombardi: 1RM = weight × reps^0.10

Run the same set through all three and you get different answers. A 100 kg set for 5 reps gives 116.7 kg on Epley, 112.5 kg on Brzycki, and 117.5 kg on Lombardi. The spread of about 5 kg is a fair illustration of how much model choice matters, and the panel on this page shows all three at once so you can see it rather than take one on faith.

Epley and Brzycki are the two most commonly used, and they have a quirk worth knowing: they agree exactly at 10 reps, both returning 133.3 kg from a 100 kg set. Below 10 reps Brzycki returns the lower estimate, and above 10 it returns the higher one. Brzycki also breaks down badly at high rep counts, since its denominator approaches zero as reps approach 37. Lombardi behaves differently again, using a power curve rather than a straight line, which makes it more forgiving at very low rep counts.

There is no correct choice among them. Pick one and use it consistently, because the value of a 1RM estimate lies in comparing it against your own previous estimates, and switching formulas mid-programme introduces a jump that has nothing to do with your strength.

Choosing the test set

Accuracy depends almost entirely on the set you feed in. The rules are simple:

• Aim for 3 to 10 reps. Fewer reps means less extrapolation and a tighter estimate. A set of 3 is considerably more informative than a set of 10.
• Take it to genuine failure, or within a rep of it. Failure means the point at which you cannot complete another rep with proper form. A set stopped three reps early will understate your max badly.
• Do not count the failed rep. Count only reps completed cleanly.
• If you get past 10, the weight was too light. Rest, add weight, and try again rather than feeding a set of 15 into the formula.

Estimates typically land within about 10% of a true tested max, which on a 100 kg lifter is a range of 10 kg. That is close enough for programming and too loose for a competition attempt.

Where the estimates go wrong

The formulas were built from data collected on people who lift, and that population skews toward trained lifters. Beginners tend to be modelled less accurately, which is unfortunate given that beginners are the ones most likely to use estimation rather than testing. Newer lifters also improve fast enough that an estimate can be out of date within weeks.

Rep tolerance varies by exercise as well. Lower-body lifts like the squat and leg press generally allow more reps at a given percentage than upper-body lifts like the bench press, so applying a single conversion table across every exercise introduces error. If you consistently hit more reps at 80% on squats than the table predicts, trust your own data over the model.

Day-to-day variation is real too. Sleep, food, hydration, caffeine, stress, and how recently you trained the same muscles can each move a maximal effort by several percent. Testing at the end of a hard training week will produce a lower number than testing after a rest day, and neither is wrong, they are simply measuring different days.

Warming up for a heavy attempt

A max attempt is won or lost before the heavy set. The pattern that works is a ramp: five to ten minutes raising your general body temperature, then a series of sets on the lift itself climbing toward the target, dropping the reps as the weight rises. A typical ramp toward a 116 kg attempt might run 40 kg for eight, 70 kg for five, 90 kg for three, 105 kg for one, then the attempt.

Two mistakes are common. The first is doing too much volume in the warm-up, which spends the energy you needed for the top set; the ramp sets exist to prepare the nervous system and rehearse the groove, not to fatigue you. The second is resting too little between the last warm-up and the attempt. Two to five minutes is not padding, it is what lets the phosphocreatine system recover enough to produce a maximal effort. Static stretching immediately before a heavy lift is worth avoiding as well, since holding a stretch for a long period temporarily reduces force output; save it for after the session.

What the number says about your training age

Absolute weight matters less than weight relative to bodyweight, which is why lifters compare in multiples. A rough map many people use for men, as multiples of bodyweight: a bench press around 0.75x is a solid novice, 1x is intermediate, and 1.5x is advanced. Squats run near 1x, 1.5x, and 2x for the same three levels, and deadlifts around 1.25x, 1.75x, and 2.5x. For women the equivalents sit near 0.5x, 0.75x, and 1x on the bench, with squats and deadlifts closer to 0.75x, 1.25x, and 1.75x.

Treat those as orientation rather than judgement. Leverages vary enormously: a lifter with short arms and a thick chest has a mechanically shorter bench press than someone with long arms, and the same weight represents different amounts of work for each. Age, injury history, and how many years you have been training all move the picture. The only comparison that reliably means anything is against your own previous numbers on the same lift.

Tracking it across a training block

The most useful way to use this calculator is not as a one-off. Log the weight and reps of your top set each session and run it through the same formula, and you get an estimated 1RM for every workout without ever attempting a true max. That series, plotted over eight or twelve weeks, tells you far more than a single test does: whether progress is linear, whether it stalls in the last week of a block, and whether a deload restores it.

Expect noise. Individual sessions bounce around by a few percent for reasons that have nothing to do with strength, so read the trend across three or four weeks rather than reacting to a single low reading. A flat trend over a full block is the signal to change something, whether that is volume, frequency, exercise selection, or recovery.

Training with your percentages

Once you have a number, the percentage tables tell you what to load for a given goal. These ranges are guidelines rather than laws, and sources differ at the margins:

% of 1RM	Reps	Sets	Primary effect
50-60%	3-5, moved fast	4-6	Explosive power, with short rests
~70%	10-15	4-6	Muscular endurance
70-80%	7-12	3-5	Muscle growth
80-100%	1-3	3-4	Maximal strength, use a spotter

One caution about the second table on this page: the rep count shown against each percentage is what you could theoretically manage at that weight, not what you should perform. Grinding out 20 reps at 60% to failure every session is a fast route to burnout. The reps you actually do at a given percentage come from your training goal, taken from the table above.

Many coaches now combine percentages with RPE, a rating of perceived exertion, or its cousin RIR, reps in reserve. A set prescribed at 8 RPE means stopping with roughly two reps left in the tank. This solves the problem percentages cannot: on a day when your max is genuinely 5% lower than usual, a fixed percentage is too heavy while an RPE target self-adjusts. Using both, a percentage as the starting point and RPE as the day's adjustment, works better than either alone.

Improving the number

Most of what raises a 1RM is unglamorous:

• Train consistently. Strength is far harder to build than to keep. Three sessions a week for a year beats six sessions a week for two months followed by nothing.
• Work heavy regularly. Maximal strength responds to loads above roughly 85%, so a programme that never goes above 70% builds other qualities instead. On a day when 85% feels impossible, training at 70% still beats skipping.
• Apply progressive overload. Add weight, reps, or sets over time. Repeating the same session indefinitely produces adaptation and then a plateau.
• Protect your form. Technique is trainable, and on the big lifts it is worth as much as extra muscle. A more efficient bar path is free weight on the bar.
• Rest properly. Muscle is built during recovery, not during the session. Chronic under-recovery flattens progress and raises injury risk, and an injury costs months.
• Sleep and eat for it. Seven to nine hours, and enough protein, generally 1.6 to 2.2 grams per kilogram of bodyweight. Strength training in a large calorie deficit is a slow way to get stronger. The Calorie Calculator sets the intake target.
• Train the supporting muscles. Weak stabilisers cap the prime movers and raise injury risk. A bench press limited by shoulder stability improves when you train the shoulders, not the chest.

When linear progress stops, varying the stimulus usually restarts it. Beyond straight sets, the common structures are supersets, where two exercises run back to back without rest, compound sets, which do the same for two exercises hitting the same muscle group, and pyramid sets, which climb in weight while dropping reps within a session. Each changes the total work and the fatigue profile, and any of them can break a plateau that stubbornly repeating the same session will not.

Keep the conditions the same

A 1RM is only comparable against another 1RM measured the same way, and small changes to the setup move the number more than people expect. Lifting shoes with a raised heel change squat depth and mechanics. A lifting belt adds meaningful weight to a squat or deadlift. Chalk changes what your grip can hold on a heavy pull. Bar type matters too, since a deadlift bar flexes more than a stiff power bar and lets you start the pull with the plates already loaded.

None of that is cheating, and all of it is worth using if you use it consistently. What breaks the comparison is testing raw in March and belted in June, then concluding you gained 10 kg of strength. Write down the equipment alongside the number.

Common mistakes

Four errors account for most bad 1RM numbers. Testing while fatigued, which understates you. Counting reps that were not clean, which overstates you. Applying one lift's max to another lift. And re-testing too often, since a maximal attempt is itself a hard training session, and testing weekly costs more in recovery than the information is worth. Every four to eight weeks is plenty.

Using this page

Enter the weight and the reps, and set the unit you lifted in. Under Settings you can choose the unit you want the answer in, which is useful if you train on kilo plates but think in pounds, and switch between the three formulas.

The panel gives the estimated max, your common training percentages from 95% down to 70%, and all three formulas side by side. The bar chart plots the weight you could theoretically move for every rep count from 1 to 20. The first table lists rep counts against weight and the matching percentage, with the row for your own test set highlighted, and the second runs the other way, from percentage to weight to the reps that weight allows. Between them they cover both questions people actually have: what should I load for a set of five, and how many reps should 80% give me.

Track the number over months rather than sessions, keep one formula, and re-test the same way each time. The Lean Body Mass Calculator and Body Fat Calculator cover the composition side of the same training.

One last thing, and it matters more than anything above: consult a qualified coach or your doctor before maximal strength testing or starting a new programme, particularly if you are new to lifting or have any injury history. The estimate on this page is a planning tool, not a target to chase into an injury.