How to Calculate Your One Rep Max (1RM) | 100 kg for 10 Reps Is What Max? 7 Formulas Compared, Charts, Rep Max Table, %1RM and Training Loads by Goal

The short answer: 1RM = weight × (1 + reps ÷ 30). 100 kg for 10 reps is about 133 kg; 80 kg for 8 is about 100 kg

Your 1RM (one rep max) is the heaviest weight you can lift for a single rep, often just called your “max”. RM stands for repetition maximum, so a 10RM is the weight you can lift exactly 10 times but not 11. If you know how many reps you could do to failure with a given weight, a prediction formula gives you a good estimate of your 1RM.

The most widely used formula is Epley’s: 1RM = weight lifted × (1 + reps ÷ 30). If you lifted 100 kg for 10 reps, that is 100 × (1 + 10 ÷ 30) ≈ 133.3 kg. If you lifted 80 kg for 8 reps, it is 80 × (1 + 8 ÷ 30) ≈ 101.3 kg.

Below we look at what the seven formulas and the NSCA chart actually say, why the formulas disagree more as reps go up, a weight × reps chart, how to work backward from your 1RM to the weight for a given number of reps, how to correct for sets you stopped short of failure, how to choose loads by goal, and how to test a real max and load the plates. All numbers use the same calculation as the 1RM calculator tool.

Seven 1RM formulas plus the NSCA chart, and how they differ

1RM formulas are empirical: researchers measured both people’s 1RM and how many reps they could do with lighter weights, then fitted an equation to the relationship. They are not derived from theory, which is why each study ended up with a slightly different shape. With W as the weight lifted and R as the reps to failure, the seven common formulas are:

Separately, the NSCA (National Strength and Conditioning Association) textbook gives a table that pairs %1RM with reps: 1 rep 100%, 2 reps 95%, 3 reps 93%, 4 reps 90%, 5 reps 87%, 6 reps 85%, 7 reps 83%, 8 reps 80%, 9 reps 77%, 10 reps 75%, 11 reps 70%, 12 reps 67% and 15 reps 65%. Divide the weight you lifted by that percentage to get your 1RM: 80 kg × 8 reps gives 80 ÷ 0.80 = 100 kg. For 13 and 14 reps, which aren’t in the table, the value is interpolated in a straight line between its neighbours.

1. 1

   Confirm the weight and reps to failure

   Example: bench press, 80 kg for 8 reps. The 9th rep didn’t go up.

2. 2

   Divide the reps by 30 and add 1

   8 ÷ 30 = 0.2667. Add 1 to get 1.2667.

3. 3

   Multiply by the weight

   80 × 1.2667 ≈ 101.3 kg. That is the Epley estimate of your 1RM.

4. 4

   Compare with other formulas and the chart

   The NSCA chart says 100 kg and the average of the seven formulas says 99.7 kg, so think of it as roughly 100 kg.

If you plug a single rep into Epley, it returns 1.033 times the weight lifted, but a weight you lifted once is, by definition, your 1RM. The tool therefore treats a single rep as the 1RM under every formula. The “average of 7 formulas” option divides by the average %1RM of the seven formulas, so converting a 1RM back to the weight for a given number of reps returns exactly the original weight.

Which formula is right? They agree at low reps and split widely past 12

At low reps, the seven formulas give almost the same answer. As reps increase, the gap widens, and at 15 or 20 reps the same set can produce 1RM estimates more than 30 kg apart. Here is the estimated 1RM for 100 kg lifted for different numbers of reps:

(Values in kg. The NSCA chart stops at 15 reps, so 20 reps is blank.)

Up to 5 reps, the formulas differ by about 7 kg, which doesn’t matter in practice. At 10 reps the spread is about 10 kg (125–135 kg), and at 20 reps the answers range from 134.9 kg (Lombardi) to 211.8 kg (Brzycki), as if they were describing different people. Brzycki and Lander have a denominator like “37 − R” that shrinks quickly as reps rise, so they blow up at high reps. Lombardi and O’Conner, by contrast, grow slowly and come out low.

• Sets of 1–5 reps: every formula gives nearly the same result. Epley or the average is plenty
• Sets of 6–10 reps: Epley, Brzycki and the NSCA chart nearly agree. The average rarely misses badly
• Sets of 11–15 reps: formulas differ by 15–30 kg. Use the average as a guide and expect a range
• Sets of 16+ reps: not suitable for estimating 1RM. Retest with a weight you fail at within 10 reps

1RM chart by weight × reps (average of 7 formulas)

Look up your estimated 1RM from the weight you lifted and your reps. Values are the average of the seven formulas, the same as the tool’s default, and apply to any lift: bench press, squat, deadlift and so on.

As the chart shows, a 100 kg bench press corresponds to roughly 80 kg × 8 or a little over 3 reps with 90 kg. 60 kg × 10 means a 1RM of about 79 kg; 70 kg × 10 means about 92 kg. Weights that aren’t listed scale proportionally: 75 kg × 8 is 99.7 kg (from 80 kg × 8) × 75 ÷ 80 ≈ 93.5 kg.

From 1RM to the weight for each rep count (rep max table): with a 100 kg max, 10 reps is about 76 kg

In training, you mostly need the reverse calculation. Once you know your 1RM, the weight you can lift for 5 or 10 reps is 1RM × %1RM. The %1RM is the formula turned around; for Epley it is 1 ÷ (1 + reps ÷ 30), so 10 reps is 1 ÷ 1.333 = 75%.

Multiply these percentages by your 1RM and round to the gym’s 2.5 kg steps, and you get this rep max table (average of 7 formulas):

With a 100 kg 1RM, sets of 10 call for 75 kg by Epley, Brzycki or the NSCA chart, and about 76.4 kg (77.5 kg rounded) by the average. These are weights at which that rep count is your limit, so for multiple sets such as “3 × 10” it is normal to start 2.5–5 kg lighter than the table so the first set isn’t already to failure.

To find how many reps you can do at a given %1RM, solve Epley the other way: reps = 30 × (100 ÷ %1RM − 1). That gives about 3.3 reps at 90%, about 5.3 at 85%, about 7.5 at 80%, exactly 10 at 75%, about 12.9 at 70% and 20 at 60%. Together with the NSCA chart, “7–8 reps at 80%” and “3–4 reps at 90%” are handy figures for planning sessions.

If you stopped short of failure, add your RIR: 80 kg × 8 with 2 left in the tank is about 105 kg

Every formula assumes reps to failure. In normal training you often stop with reps in hand, before your form breaks down or when nobody is spotting you. If you enter such a set as is, you will underestimate your 1RM.

That is where RIR (reps in reserve: how many more reps you could have done) comes in. If you stopped at 8 and felt you had 2 more, that is RIR 2, so you calculate with 8 + 2 = 10 reps to failure. For 80 kg × 8 at RIR 2, treat it as 80 kg × 10: 106.7 kg by Epley and 104.7 kg by the average. That is about 5 kg higher than the same 8 reps taken to failure (99.7 kg on average).

RPE (rating of perceived exertion) describes effort on a 10-point scale: RPE 10 is failure and RPE 8 is about two reps left (RIR 2). Less experienced lifters tend to underestimate how much they have left, so it is safest to use RIR only up to 3. Estimating a 1RM from a set at RIR 4 or higher adds a lot of error.

Loads and reps by goal: 85%+ for strength, 67–85% for hypertrophy

The main reason to know your 1RM is to set training loads. In the NSCA framework, the %1RM, rep range and rest between sets depend on the quality you want to build.

The common advice for hypertrophy, “a weight you fail at in 8–10 reps”, works out to 75–80% of 1RM: 75–80 kg with a 100 kg max, or 45–47.5 kg with a 60 kg max. Many recent studies also show that lighter loads build muscle when sets are taken close to failure, so what matters more than the exact load is doing enough hard sets near your limit.

• Beginners should start at 60–70% for 10–15 reps to groove their technique
• To track progress, log a set that reaches failure around 5 reps on the same lift with the same technique each time
• Converting logs to 1RM lets you compare sets with different reps, such as “80 kg × 6 last month, 82.5 kg × 5 this month”
• Logging your body weight too lets you follow progress as a ratio (1RM ÷ body weight)

How to test a true 1RM: warm up in steps at 50%, 70% and 85%

If you want a measured 1RM rather than an estimate, don’t jump straight to a heavy weight; work up in steps. The tool’s warm-up guide for a day when you attempt a single at the target weight looks like this:

1. 1

   Set a target from your estimate

   Estimate your 1RM from a recent set and aim at that value or a little below. On your first test, start at about 95% of the estimate.

2. 2

   Add weight while cutting reps

   Reduce reps as the weight goes up so you don’t accumulate fatigue. Rest 2–3 minutes between sets and 3–5 minutes from 85% up.

3. 3

   Attempt the target once

   If it goes, add 2.5–5 kg and try again. If you miss, stop there for the day. Three attempts is a sensible limit.

4. 4

   Make it safe

   For bench press and squat, use a spotter or set the safety bars at the right height.

Loading the bar for your target weight, and converting kg and lb

Once you have a weight, load the bar. The weight per side is (target − bar) ÷ 2 − collar, made up from your available plates with as few plates as possible. A standard gym barbell (Olympic bar) weighs 20 kg.

Videos and apps from the US often use pounds (lb); 1 lb = 0.45359237 kg. American gym bars weigh 45 lb (about 20.4 kg), and lifters describe weights by how many 45 lb plates are on each side.

To go from kg to lb, multiply by 2.2046: 60 kg is about 132.3 lb, 100 kg is about 220.5 lb and 140 kg is about 308.6 lb. Remembering that a 225 lb bench is a little over 100 kg makes lifting numbers from other countries easier to read.

When estimates go wrong, and other cautions

• Differences between lifts: at the same %1RM, lower-body lifts such as squats and leg presses tend to allow more reps than the bench press. A 1RM estimated from a high-rep lower-body set tends to come out high
• Individual differences: muscle fibre type (fast-twitch vs slow-twitch) and training history mean two people with the same 1RM can differ by several reps. The more endurance you have, the more rep-based estimates overstate your 1RM
• Technique: bouncing the bar off your chest on the bench or cutting squat depth makes sets incomparable from one session to the next
• Fatigue: sets done after other exercises underestimate your 1RM. Take the set you estimate from as your first main working set of that lift
• Machines vs free weights: machine weight stacks vary by manufacturer and pulley ratio and can’t be compared with a free-weight 1RM

In short, treat an estimate as accurate to about ±5%. It is most useful as a way to track progress for the same person on the same lift with the same technique. If you also want to follow changes in body weight and build, see how to calculate BMI; to set how much to eat while cutting, see how to calculate basal metabolic rate.

FAQ

If I can lift 100 kg for 10 reps, what is my 1RM?

Epley, Brzycki and the NSCA chart all give 133.3 kg. O’Conner comes out lower at 125 kg, and the average of the seven formulas is 130.9 kg. Realistically, think of it as somewhere between 125 and 135 kg.

If I bench 80 kg for 8 reps, what is my max?

About 99.7 kg by the average of seven formulas, 101.3 kg by Epley and exactly 100 kg by the NSCA chart (8 reps = 80%). “80 kg for 8 means a 100 kg bench” is a handy rule. If you had two reps left (RIR 2), calculate it as 10 reps for about 105 kg.

Which 1RM formula should I use?

For sets of 1–10 reps, the widely used Epley formula (weight × (1 + reps ÷ 30)) or the average of the seven formulas is enough; up to 10 reps they all fall within about 10 kg. Beyond 12 reps, Brzycki and Lander come out far too high and Lombardi and O’Conner too low, so use the average or retest with a weight you fail at within 10 reps.

My 1RM is 100 kg. What weight should I use for sets of 10?

75 kg by Epley, Brzycki or the NSCA chart, and about 76.4 kg by the average of seven formulas. For 5 reps it is about 85–89 kg, and for 8 reps about 80 kg. For multiple sets, start 2.5–5 kg lighter than those numbers.

How many reps can I do at 80% of my 1RM?

About 8 by the NSCA chart and 7–8 by inverting Epley. At 90% expect 3–4 reps, at 85% 5–6, at 75% about 10 and at 70% 11–13.

What %1RM and reps should I use for hypertrophy?

The NSCA guideline for hypertrophy is 67–85% for 6–12 reps with 30 seconds to 1.5 minutes of rest. The popular “weight you fail at in 8–10 reps” is 75–80%, or 75–80 kg for someone with a 100 kg max. For strength, use 85% or more for 1–5 reps; for muscular endurance, 67% or less for 12 or more.

Is it OK to estimate my 1RM from a set of 15 or 20 reps?

It isn’t recommended. From 100 kg × 20, the formulas give anything from 134.9 kg to 211.8 kg. The more reps you do, the more endurance matters and the weaker the link to your 1RM. Retest with a weight that takes you to failure in 3–8 reps.

How many kg is 225 lb?

About 102.1 kg (1 lb = 0.45359237 kg). It is a 45 lb bar with two 45 lb plates on each side, often called “two plates”. 135 lb (one plate per side) is about 61.2 kg and 315 lb (three per side) is about 142.9 kg.