One-Rep Max (1RM): How to Estimate, Test and Use It

What is a one-rep max?

A one-rep max is the most weight you can lift for a single repetition of a specific exercise, with full range of motion and without breaking technique. It is specific to each lift: your squat 1RM tells you nothing precise about your bench press, and even changing the grip, stance or depth changes the number.

Your 1RM is also not fixed. It rises with training and can dip from day to day with sleep, stress and fatigue. That said, when conditions are similar, it's a very consistent measurement: a 2020 systematic review by Grgic and colleagues found good-to-excellent test–retest reliability for 1RM testing across ages, sexes, training levels and exercises, with a median intraclass correlation of 0.97.

Lifters use 1RM for two main reasons: to track strength over time and to set training loads as percentages of their maximum.

Estimating vs testing your 1RM

You can find your 1RM in two ways: lift progressively heavier singles until you reach your limit, or perform a hard set of several reps and plug the numbers into a formula. Each approach has its place.

For most people who train for health, muscle or general strength, estimating is enough. Direct testing makes most sense for powerlifters, for experienced lifters who want an exact benchmark, and for people following programs built around tested maxes.

• Estimating: less fatigue and lower risk, fits into a normal workout, and can be updated every few weeks from your regular training sets.
• Estimating drawbacks: less precise, especially with higher reps, and depends on how close to failure the set really was.
• Testing: the most accurate number and good practice at handling heavy loads.
• Testing drawbacks: more fatigue, needs solid technique and a safe setup, and a missed attempt carries more risk.

1RM formulas: Epley, Brzycki and Lombardi

Several equations turn a set of reps into an estimated 1RM. The two most widely used are Epley, 1RM = weight × (1 + reps ÷ 30), and Brzycki, 1RM = weight × 36 ÷ (37 − reps). Lombardi, 1RM = weight × reps raised to the power of 0.1, is another common option. For a single rep, all three simply return the weight lifted.

Take 100 kg lifted for 5 reps. Epley gives about 116.7 kg, Brzycki 112.5 kg and Lombardi about 117.5 kg, for an average of roughly 115.6 kg. The formulas agree closely at low reps and drift apart as reps rise, which is why our one-rep max calculator shows each result and uses their average as the headline figure.

Our calculator accepts sets of up to 12 reps and flags results above 10 reps as less accurate. It also shows a percentage table so you can turn your estimate straight into training loads.

How accurate are 1RM estimates?

Estimates work best when the set is heavy and close to failure. In a 2006 study by Reynolds and colleagues, a 5-rep max predicted 1RM more accurately than 10- or 20-rep maxes, and the authors concluded that no more than 10 reps should be used in these equations. Beyond that, endurance, pacing and fatigue tolerance start to play a bigger role than maximal strength.

People also differ in how many reps they can do at a given percentage of their max. A 2024 meta-regression by Nuzzo and colleagues, covering data from over 7,000 people, found wide individual variation and more reps at the same relative load on the leg press than on the bench press, while sex, age and training status had little influence. So treat any estimate as a good approximation, not an exact value.

• Use a set of about 3–8 reps for the best estimate, and no more than 10.
• The set should be close to failure. If you stopped with reps left, a common approach is to add those reps in reserve to the reps you did before calculating.
• Use a set done fresh, early in the workout, not after several fatiguing sets.
• Compare estimates over time with the same exercise, technique and rep range.

How to test your 1RM safely

Only test a true max on exercises you perform with consistent, confident technique, after at least several months of regular training. Test when you're rested, not at the end of a hard week, and plan for a session of 30–45 minutes, most of which is warm-up and rest.

Use a squat rack with safety pins or straps set just below the bottom of your range of motion, and bench press with safety arms or an experienced spotter. Warm up gradually with fewer reps as the weight climbs, and rest 3–5 minutes between heavy singles. Aim to reach your max within about three to five heavy attempts after the warm-up, so fatigue doesn't cap the result.

• 5–10 minutes of light general warm-up, then the empty bar for 8–10 reps.
• About 50% of your expected max for 5 reps, then about 70% for 3 reps.
• About 80% for 1–2 reps, then about 90% for 1 rep.
• First attempt at about 95–100% of your expected max, then add 2–5% for each further attempt.
• Stop when technique clearly breaks down or the bar speed becomes very slow; a grinding rep with poor form doesn't count.

Using percentages of 1RM to program training

Once you know your 1RM, you can prescribe loads as percentages of it. The relationship between load and reps is roughly predictable, and our calculator's load table uses an inverse of the Epley formula to show about how many reps you can expect at each percentage.

Most strength programs use loads around 80–90% or more for sets of 1–6 reps, while muscle-building work typically uses about 60–80% for 6–15 reps, taken close to failure. Because individual rep capacity varies, use the percentages as a starting point and adjust based on how the sets actually feel. Re-estimate your 1RM every 4–8 weeks, or whenever your working sets start to feel clearly easier.

• 90% of 1RM: about 3 reps.
• 85%: about 5 reps.
• 80%: about 8 reps.
• 75%: about 10 reps.
• 70%: about 13 reps.

RPE and RIR: an alternative to percentages

Effort-based scales let you adjust loads to how strong you are on the day. The resistance-training RPE scale developed by Zourdos and colleagues in 2016 links each rating to repetitions in reserve (RIR): RPE 10 means no reps left, RPE 9 means one rep left, RPE 8 means two and so on. In that study, experienced lifters rated their effort more accurately at 1RM than novices, and their ratings tracked bar speed more closely.

Helms and colleagues suggest combining both approaches, for example 3 sets of 5 at about 80% of 1RM or RPE 8, and practising the scale before relying on it. If you're a beginner, you don't need to max test at all: pick a rep range, stop sets with 1–3 reps in reserve and add weight gradually. Your estimated 1RM from training sets will rise on its own.