One Rep Max Calculator

What a One Rep Max (1RM) Is (and Why You’d Estimate It)

ProcalcAI’s One Rep Max Calculator estimates your 1RM using the Epley formula, a widely used strength-training equation that converts a weight-and-reps performance into an estimated max. Along with your estimated 1RM, the calculator also gives you training loads at approximately 90 percent, 80 percent, and 70 percent—handy for planning heavy, moderate, and technique-focused work.

This estimate is most reliable when the set is performed close to failure with consistent technique and a reasonable rep range (often around 2–10 reps). Extremely high reps can skew results because muscular endurance becomes a bigger factor than maximal strength.

The Epley Formula Used in This Calculator

Estimated 1RM = Weight Lifted × (1 + Reps Completed ÷ 30)

Where: - Weight Lifted is the load you used for your set. - Reps Completed is how many clean reps you performed.

Special case: - If Reps Completed = 1, then 1RM = Weight Lifted (because you already did a single).

The calculator then computes three common training percentages from your estimated 1RM: - 90 percent load = 1RM × 0.90 - 80 percent load = 1RM × 0.80 - 70 percent load = 1RM × 0.70

Rounding behavior (important if you’re checking by hand): - The estimated 1RM is rounded to the nearest 0.1 (one decimal place). - The percentage loads are rounded to the nearest whole number.

These percentages are not “magic,” but they’re a practical way to translate your estimated max into repeatable training weights.

How to Calculate Your 1RM Step by Step

### Step 1: Enter your Weight Lifted Input the load you actually used for the set. Use the same unit you train with (kg or lb). The math works the same either way—just stay consistent.

### Step 2: Enter your Reps Completed Enter the number of full reps you completed with solid technique. If you stopped because form broke down, use the last rep that was clearly valid.

### Step 3: Apply the Epley formula Compute:

1RM = Weight × (1 + Reps/30)

If reps = 1, then 1RM = Weight.

### Step 4: (Optional) Calculate training loads at 90/80/70 percent Once you have your estimated 1RM: - 90 percent = 1RM × 0.90 - 80 percent = 1RM × 0.80 - 70 percent = 1RM × 0.70

These are useful anchors for programming: - 90 percent often aligns with heavy doubles/singles practice (depending on the lifter). - 80 percent is common for strength-focused volume. - 70 percent is frequently used for technique work, speed work, or higher-rep hypertrophy sets.

Worked Examples (with Real Numbers)

### Example 1: 100 for 5 reps 1) Weight = 100 2) Reps = 5 3) Epley estimate:

1RM = 100 × (1 + 5/30) 1RM = 100 × (1 + 0.1667) 1RM = 100 × 1.1667 1RM ≈ 116.7

Training loads: - 90 percent ≈ 116.7 × 0.90 = 105.03 → 105 - 80 percent ≈ 116.7 × 0.80 = 93.36 → 93 - 70 percent ≈ 116.7 × 0.70 = 81.69 → 82

So you’d plan around 105 (heavy), 93 (moderate), 82 (lighter/technique).

### Example 2: 140 for 3 reps 1) Weight = 140 2) Reps = 3 3) Epley estimate:

1RM = 140 × (1 + 3/30) 1RM = 140 × (1 + 0.1) 1RM = 140 × 1.1 1RM = 154.0

Training loads: - 90 percent = 154.0 × 0.90 = 138.6 → 139 - 80 percent = 154.0 × 0.80 = 123.2 → 123 - 70 percent = 154.0 × 0.70 = 107.8 → 108

This shows why triples are a popular choice for estimating strength: the rep count is low enough to reflect strength more than endurance.

### Example 3: 60 for 10 reps 1) Weight = 60 2) Reps = 10 3) Epley estimate:

1RM = 60 × (1 + 10/30) 1RM = 60 × (1 + 0.3333) 1RM = 60 × 1.3333 1RM ≈ 80.0

Training loads: - 90 percent = 80.0 × 0.90 = 72.0 → 72 - 80 percent = 80.0 × 0.80 = 64.0 → 64 - 70 percent = 80.0 × 0.70 = 56.0 → 56

This can be a reasonable estimate, but keep in mind: at 10 reps, fatigue tolerance and pacing can influence the result more than with 3–5 reps.

Pro Tips for Getting a More Accurate 1RM Estimate

Common Mistakes (and How to Avoid Them)

Used well, a 1RM estimate is a simple way to track progress, set training loads, and compare performance across rep ranges—without needing to grind maximal singles every time you want to plan your next block.

Authoritative Sources

This calculator uses formulas and reference data drawn from the following sources:

- CDC — Physical Activity - NIH — National Heart, Lung, and Blood Institute - CDC — Healthy Weight

This one rep max calculator uses standard fitness formulas to compute results. Enter your values and the formula is applied automatically — all math is handled for you. The calculation follows industry-standard methodology.

• https://www.acsm.org
• https://pubmed.ncbi.nlm.nih.gov