What is a 1-rep max (1RM)?

A 1-rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise with correct form. It is the standard measure of maximal strength used in powerlifting, weightlifting, and strength training programming.

What is the Epley formula?

The Epley formula estimates 1RM as: 1RM = weight × (1 + reps / 30). It was published by Boyd Epley in 1985 and is one of the most widely used prediction formulas.

What is the Brzycki formula?

The Brzycki formula estimates 1RM as: 1RM = weight × (36 / (37 − reps)). It was published by Matt Brzycki in 1993. It cannot be used above 36 reps.

How accurate are 1RM prediction formulas?

Both Epley and Brzycki formulas are most reliable at 1–6 reps and less reliable above 10 reps. Individual differences in muscle fiber composition, fatigue resistance, and technique affect how well a formula predicts actual 1RM.

What percentage of 1RM should I train at?

Training percentage depends on your goal: heavy strength work typically uses 85–95% of 1RM for 1–5 reps; hypertrophy work typically uses 65–80% for 6–12 reps; muscular endurance work uses 50–65% for 15+ reps. These are general guidelines, not prescriptions.

Should I test my actual 1RM instead of estimating it?

For most people, especially beginners, estimating from a submaximal set is safer and more practical than attempting a true 1RM test, which carries injury risk if form breaks down under maximum load.

1-Rep Max Calculator — Strength Estimator

1-Rep Max Estimator

These tools show measurements and calculations — not health advice. Results are mathematical outputs based on the inputs you provide. Individual factors such as body composition, medical history, and fitness level affect what any number means for you. Consult a qualified professional before making decisions about your health or training.

Your 1-rep max (1RM) is the maximum weight you can lift for a single repetition with correct form. Knowing it lets you set training weights as a percentage of your maximum — a method used in strength and power programming. This estimator uses two published prediction formulas (Epley 1985 and Brzycki 1993) to derive an estimate from a submaximal set you've already done.

The formulas

Epley (1985):

1RM = weight × (1 + reps / 30)

Brzycki (1993):

1RM = weight × (36 / (37 − reps))

Where weight is the load you lifted and reps is the number of repetitions completed. Both formulas are most accurate at 1–6 reps and become progressively less reliable above 10 reps.

Practical examples

Example 1 — Estimating from a 5-rep set: You bench pressed 185 lbs for 5 reps.

Epley: 185 × (1 + 5/30) = 185 × 1.167 = 215.8 lbs
Brzycki: 185 × (36 / 32) = 185 × 1.125 = 208.1 lbs A reasonable working estimate is 208–216 lbs.

Example 2 — Programming from the estimate: With an estimated 1RM of 215 lbs, 80% = 172 lbs (a typical hypertrophy load for 6–10 reps).

Example 3 — Using kilograms: You squatted 100 kg for 3 reps.

Epley: 100 × (1 + 3/30) = 100 × 1.1 = 110 kg
Brzycki: 100 × (36 / 34) = 100 × 1.059 = 105.9 kg

Common mistakes

Testing above 10 reps and trusting the result. Both formulas are derived from data at low rep ranges. At 12–15 reps, the estimates diverge more from true 1RM because muscular endurance becomes a larger factor than maximal strength.

Treating the estimate as a guaranteed maximum. The formulas give a statistical average, not a personal guarantee. Individual variation in fiber type, fatigue, technique, and rest time all affect where your actual 1RM falls.

Using bodyweight-dependent exercises. Push-ups, pull-ups, and dips involve your bodyweight. These formulas are designed for barbell or machine lifts where the load is fixed and measurable.

Testing every session. You do not need to know your 1RM precisely to train. Many strength programs use training percentages based on a training max — typically 90% of an estimated 1RM — to keep intensity manageable and technique safe.

International and regional variations

Formula	Origin	Notes
Epley (1985)	University of Nebraska, USA	Widely used; slightly overestimates at higher rep ranges
Brzycki (1993)	Princeton University, USA	More conservative; mathematically undefined above 36 reps
Lombardi (1989)	USA	1RM = weight × reps^0.10; tends to underestimate at low reps
O'Conner et al. (1989)	USA	1RM = weight × (1 + 0.025 × reps); linear, less sensitive

Quick reference — percentage of 1RM

% of 1RM	Typical reps	Training goal
95–100%	1	Maximal strength testing
85–94%	2–5	Strength development
75–84%	6–8	Strength-hypertrophy overlap
65–74%	9–12	Hypertrophy
50–64%	13–20+	Muscular endurance

For a reference covering body fat percentage ranges by sex and measurement method accuracy, see the Body Fat Percentage Reference Chart →.

Unit:

Weight lifted (lbs)

Reps completed (1–36)

Enter weight and reps (1–36) to estimate your 1-rep max.

Estimated values only — not a training prescription. Accuracy decreases above 10 reps. Epley (1985) and Brzycki (1993) formulas.

Frequently Asked Questions

What is a 1-rep max (1RM)?: A 1-rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise with correct form. It is the standard measure of maximal strength used in powerlifting, weightlifting, and strength training programming.
What is the Epley formula?: The Epley formula estimates 1RM as: 1RM = weight × (1 + reps / 30). It was published by Boyd Epley in 1985 and is one of the most widely used prediction formulas.
What is the Brzycki formula?: The Brzycki formula estimates 1RM as: 1RM = weight × (36 / (37 − reps)). It was published by Matt Brzycki in 1993. It cannot be used above 36 reps.
How accurate are 1RM prediction formulas?: Both Epley and Brzycki formulas are most reliable at 1–6 reps and less reliable above 10 reps. Individual differences in muscle fiber composition, fatigue resistance, and technique affect how well a formula predicts actual 1RM.
What percentage of 1RM should I train at?: Training percentage depends on your goal: heavy strength work typically uses 85–95% of 1RM for 1–5 reps; hypertrophy work typically uses 65–80% for 6–12 reps; muscular endurance work uses 50–65% for 15+ reps. These are general guidelines, not prescriptions.
Should I test my actual 1RM instead of estimating it?: For most people, especially beginners, estimating from a submaximal set is safer and more practical than attempting a true 1RM test, which carries injury risk if form breaks down under maximum load.