One Rep Max Calculator (1RM): Estimate Your Max

Q: How many reps of 185 lb do I need to bench 225?

About 6 to 7 reps of 185 lb estimates a 225 lb bench press max using the Epley formula. The reverse 1RM calculator on this page works this out for any set weight and target in one step.

Q: How many reps of 225 lb do I need to bench 315?

About 12 reps of 225 lb estimates a 315 lb bench press max with the Epley formula (225 x (1 + 12 / 30) = 315). That is a heavy, high-rep set, so use a spotter on every rep.

Q: What percentage of my 1RM should I use for training?

A common starting point is 70% of 1RM for 8 to 10 reps, 80% for about 5 reps, and 90% for 2 to 3 reps. The percentage chart under your result shows weights from 55% to 95% with a typical rep range for each, ready to plan a workout around.

1rm calculator, one rep max calculator, strength training, Bill Starr

Calculate your one-rep max (1RM) for any lift. Your one-rep max is the max weight you can lift for a single repetition for a given exercise.

Your one rep max (1RM) is the heaviest weight you can lift for a single clean repetition. This one rep max calculator estimates your max from any recent set: enter the weight and reps below and it returns predictions from six proven formulas, a percentage chart for planning your loads, and an RPE adjustment for how hard the set felt.

Bill Starr built his entire strength philosophy around the idea that you should know exactly what your working weights mean in relation to your top strength. The one rep max calculator on this page is the tool he would have reached for: it turns any set into a number you can plan around. For the classic programming that grew out of this thinking, see Bill Starr's 5x5 Program.

1RM Calculator

Estimate your one-rep max from any set you have lifted recently.

Estimated 1RM

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Formula comparison

Formula	Estimated 1RM

1RM percentage chart

% of 1RM	Weight (lb)	Typical rep range

Training max

Training max %

Estimated training max: —

A training max is a programming number (by default 90% of your 1RM), not the same as a tested one-rep max.

Estimated rep maxes

Advanced options

RPE adjuster

Rate-of-perceived-exertion (RPE) adjusts the estimate when a set was harder or easier than maximal. RPE 10 is maximal, RPE 9 leaves about 1 rep in reserve, RPE 8 about 2. Because RPE is subjective, the result is a rough estimate, not a precise number.

Set RPE

RPE-adjusted 1RM estimate: —

Reverse 1RM calculator

Enter a target one-rep max and a weight to see roughly how many reps that weight would need to reach the target (e.g., “how many reps of 185 lb to reach a 225 lb bench”).

Target 1RM

Weight for the set

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Plate loader

See which plates go on each side of a standard 45 lb (20 kg) bar to reach a target weight.

Target barbell weight

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How a One Rep Max Calculator Works

A 1RM calculator takes the weight you lifted, the number of reps you completed, and applies a formula that extrapolates to a single maximum rep. The logic is simple: the more reps you do with a given weight, the lighter that weight is relative to your true max, so the higher the calculator pushes the estimate.

For example, 225 lb x 5 estimates a one rep max of about 260 lb. Ask the same calculator for 225 lb x 10 and it estimates roughly 294 lb, because ten reps of 225 means the weight is a much lower percentage of your actual strength. That relationship is what the famous one rep max formulas encode.

The Six One Rep Max Formulas

Formula	Idea behind it
Epley	The most common default: add one-thirtieth of the weight for each rep over one.
Brzycki	Developed for collegiate athletes; tends to estimate lower for higher reps, which can be more conservative.
Lombardi	Uses reps raised to a fractional power, estimating slightly higher as reps climb.
O'Conner et al.	Similar structure to Epley with a gentler slope, common in fitness-testing literature.
Wathan	An exponential model fitted to a large bench press sample.
NASM	The equation published by the National Academy of Sports Medicine: weight + (weight × reps ÷ 30.48). Nearly identical to Epley with a slightly larger rep constant.

Because each formula was built from different data, they disagree by a few percent. The calculator highlights Epley and averages all six, giving you a single working number without pretending any one formula is perfect.

Why the Result Is an Estimate

Every one rep max formula is an estimate, not a measurement. Actual maximum strength depends on bar speed, fatigue, technique, and even the time of day. A calculator also cannot know the difference between five fast reps and five grinding reps. That is why the results on this page are labeled estimates and why programming advice built on them uses a training max (90% of your estimated 1RM by default) rather than the raw number.

RPE and RIR: Adjusting the Estimate for Effort

RPE (rate of perceived exertion) tells you how hard a set felt: 10 means maximal effort, 9 leaves about one rep in reserve, and 8 leaves roughly two. The calculator's RPE adjuster rebuilds your estimate from your reps plus the reserve reps you left in the tank. Because RPE is subjective, treat the adjusted result as a directional number, not a measurement.

Training Max vs. Tested Max

A tested 1RM is a personal record and a risky thing to chase every week. A training max is a programming number, by default 90% of your 1RM, that you progress against without grinding yourself into the ground. Starr's 5x5 programming is built exactly this way: consistent, progressive, repeatable work instead of constant max attempts.

How to Test a 1RM Safely (If You Must)

If you do decide to test a true max, warm up in increasing singles, use a spotter on the bench and safeties in the rack on the squat, and stop the moment technique breaks. Most lifters never need a genuine max: a last heavy triple with an honest effort, put into this calculator, gives you the same planning number with far less risk. For the squat specifically, get the rack setup right first — see low bar squat form and bar placement.

Bench, Squat, and Deadlift 1RM Estimates

Use the exercise drop-down in the calculator to label your lift. The formulas themselves are lift-agnostic — the same math estimates a bench press max, squat max, or deadlift max from your own set — but keeping the label attached means your log stays honest. Pressing questions behave slightly differently from the hips-driven lifts, which is one reason the calculator shows a range of formulas instead of one rigid answer. For press technique, see The Press, Part 1 by Bill Starr; for the pull, Deadlift, Part 1.

The 1RM Percentage Chart

The percentage table under your result shows what weights to handle for different rep ranges. Working at 70% of your 1RM typically lands around 8-10 reps, 80% around five, and 90% around two or three. That chart is the bridge between knowing your max and structuring a workout around it, and it is exactly the kind of planning table Starr used in The Strongest Shall Survive.

Frequently Asked Questions

What is a one rep max?

A one rep max (1RM) is the heaviest weight you can lift for a single clean repetition with good form. It is exercise-specific, so your bench press max differs from your squat max. You can estimate it from a heavier, lower-rep set instead of risking a true max attempt.

How do you calculate a one rep max?

Enter the weight you lifted and the reps you completed. Each formula (Epley, Brzycki, Lombardi, O'Conner, Wathan, and NASM) estimates your 1RM from that set. The calculator shows all six and their average, with Epley highlighted as the common default. For example, 225 lb for 5 reps estimates a one rep max of about 260 lb.

Which one rep max formula is most accurate?

No formula is universally the most accurate; each was fitted to a different data set. In the 1 to 10 rep range, Epley and Brzycki perform best in most comparisons, and averaging several formulas typically reduces error. Use the average as your working number and a more conservative estimate for programming.

What is the difference between the Epley and Brzycki formulas?

Epley is 1RM = weight x (1 + reps / 30), and Brzycki is 1RM = weight x 36 / (37 - reps). They give nearly identical results around 10 reps; below that, Epley usually estimates a little higher while Brzycki runs slightly more conservative, especially at 5 reps and under.

How many reps of 185 lb do I need to bench 225?

About 6-7 reps of 185 lb estimates a 225 lb bench press max using the Epley formula. The reverse 1RM calculator on this page works this out for any set weight and target in one step.

How many reps of 225 lb do I need to bench 315?

About 12 reps of 225 lb estimates a 315 lb bench press max with the Epley formula (225 x (1 + 12 / 30) = 315). That is a heavy, high-rep set, so use a spotter on every rep.

What is RPE and how does it affect my 1RM estimate?

RPE (rate of perceived exertion) rates how hard a set felt: 10 is maximal effort, 9 leaves about one rep in reserve, and 8 leaves about two. The RPE adjuster adds those reserve reps back into the estimate. Because RPE is subjective, it refines an estimate but does not make it precise.

How do I convert a 3RM, 5RM, or 10RM to a 1RM?

Use the estimated rep max chips under the result: from your 1RM they show roughly what a 2RM, 3RM, 5RM, 8RM, and 10RM should weigh. To go the other way, enter a known 3RM, 5RM, or 10RM into the calculator to estimate the 1RM it corresponds to.

What is a training max?

A training max is a programming number, by default 90% of your estimated 1RM, that you progress against each week. It keeps the workload repeatable and avoids grinding yourself to failure, which is how Bill Starr built his 5x5 programming: consistent, progressive, plan-driven work.

What percentage of my 1RM should I use for training?

A common starting point is 70% of 1RM for 8-10 reps, 80% for about 5 reps, and 90% for 2-3 reps. The percentage chart under your result shows weights from 55% to 95% with a typical rep range for each, ready to plan a workout around.

How should I test my 1RM safely?

Warm up thoroughly, build up in increasing singles, and use a spotter on the bench and safeties in the rack on the squat. Stop the moment your form breaks down. Most lifters never need a true max: an honest heavy triple fed into this calculator gives the same planning number with far less risk.