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One Rep Max Calculator — Epley & Brzycki 1RM Estimator

Enter the weight and reps from a single working set to estimate your one-rep max (1RM) using two well-known strength formulas side by side, plus a ready-made percentage chart for planning training loads.

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🏋️ Enter Your Set

Epley: 1RM = Weight × (1 + Reps ÷ 30)
Brzycki: 1RM = Weight × 36 ÷ (37 − Reps)

📊 Estimated 1RM

Enter your weight and reps, then calculate
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Disclaimer: This calculator provides an educational, fitness-tracking estimate only, not personal training or medical advice. Actual one-rep max varies with lifting technique, fatigue, injury history, and individual physiology. Warm up properly, consider working with a qualified coach before attempting a true 1RM test, and consult a doctor before starting any new strength program if you have an existing health condition.

How This Calculator Works

Testing a true one-rep max — the single heaviest weight you can lift once with correct form — is fatiguing and carries injury risk, especially for lifts near your limit. Instead, most lifters estimate their 1RM from a lighter set taken close to failure, using a prediction formula built from real strength-training data. This tool runs your numbers through two of the most widely used formulas, Epley and Brzycki, so you can compare them rather than relying on a single estimate.

The Epley Formula

1RM = Weight × (1 + Reps ÷ 30). Epley's formula assumes a fairly steady, linear drop-off in the weight you can lift as reps increase, which is why it stays mathematically valid even at high rep counts (20, 30, or more) where other formulas break down.

The Brzycki Formula

1RM = Weight × 36 ÷ (37 − Reps). Brzycki's formula assumes strength drops off a little faster as reps climb, and it becomes undefined once reps reach 37, since the denominator (37 − Reps) hits zero. For sets in the typical 1-10 rep range used for most 1RM estimates, Brzycki and Epley usually land close together.

Worked Example

Say you lifted 100 kg for 5 reps:

The two estimates differ by a few kilograms here, which is typical — treat the range between them as a realistic window for your true max rather than fixating on one exact number.

Training Load Percentages

Once you have an estimated 1RM, training programs typically prescribe working weights as a percentage of it rather than a fixed number, so the percentage table updates automatically whenever your estimate changes. Lower percentages (60-75%) are common for higher-rep, muscle-building work; higher percentages (85-95%) are typically reserved for low-rep strength and power phases, usually programmed by an experienced coach.

Frequently Asked Questions

Both formulas were built by fitting curves to real lifting data, but the researchers used different rep ranges and assumptions about how strength drops off as reps climb. Epley tends to assume a steadier decline and stays usable at higher rep counts, while Brzycki assumes a sharper drop-off that becomes unreliable and mathematically undefined past 36 reps. For sets under about 10 reps, the two formulas are usually within a few percent of each other.
Estimated 1RM is a projection, not a measurement — it's typically most reliable when the set used to calculate it was 3 to 8 reps, taken close to failure with good form. Estimates from very high-rep sets (15+) or sets that weren't taken near failure tend to drift further from your true max, since fatigue and technique breakdown affect low-rep and high-rep strength differently.
Strength training programs are commonly built around percentages of your 1RM rather than a fixed weight — for example, a hypertrophy block might use 70-80% for higher-rep sets, while a strength or power phase might call for 85-95%. Recalculating these percentages whenever your estimated 1RM changes keeps your training weights aligned with your current strength instead of a number from months ago.
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