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One Rep Max Calculator

Estimate 1RM from weight and reps (Epley). Free online One Rep Max Calculator for health — instant, accurate results, mobile-friendly, no signup needed.

1RM
116.666667

Derivation

  1. ├── 01Givenw = 100, reps = 5
  2. ├── 02Formulae.w × (1+e.reps / 30)
  3. ├── 03Substitutee.100 × (1+e.5 / 30)
  4. └── 04Compute 1RM116.666667
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§01What is

Understanding the One Rep Max Calculator

The One Rep Max Calculator computes 1RM from 2 inputs: weight lifted, reps. Estimate 1RM from weight and reps (Epley).

Health metrics give us objective checkpoints against a body that can feel unreliable. Used alongside professional guidance — not in place of it — these numbers help you track progress and spot trends that matter. The One Rep Max Calculator sits in that toolkit — it estimate 1RM from weight and reps (Epley). Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

e.w × (1+e.reps / 30)

Where

w
Weight lifted
reps
Reps
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Weight lifted = 100, Reps = 5.

  1. 01Start by noting the input — Weight lifted: 100.
  2. 02Start by noting the input — Reps: 5.
  3. 03Substitute these values into the formula: e.w × (1+e.reps / 30)
  4. 04Compute 1RM: the calculator returns 116.667.
  5. 05Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common One Rep Max Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Weight lifted halved

w = 50 (from 100)

Keep every other input at its default and halve the weight lifted. See how 1rm responds.

  1. 01New Weight lifted: 50
  2. 02Baseline 1RM: 116.667
  3. 03New 1RM: 58.3333
  4. 041RM decreases by 50% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Weight lifted doubled

w = 200 (from 100)

Keep every other input at its default and double the weight lifted. See how 1rm responds.

  1. 01New Weight lifted: 200
  2. 02Baseline 1RM: 116.667
  3. 03New 1RM: 233.333
  4. 041RM increases by 100% → use this sensitivity to plan for real-world variation.
03 · PATTERN

Reps halved

reps = 2.5 (from 5)

Keep every other input at its default and halve the reps. See how 1rm responds.

  1. 01New Reps: 2.5
  2. 02Baseline 1RM: 116.667
  3. 03New 1RM: 108.333
  4. 041RM decreases by 7.1% → use this sensitivity to plan for real-world variation.
04 · PATTERN

Reps doubled

reps = 10 (from 5)

Keep every other input at its default and double the reps. See how 1rm responds.

  1. 01New Reps: 10
  2. 02Baseline 1RM: 116.667
  3. 03New 1RM: 133.333
  4. 041RM increases by 14.3% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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