One Rep Max (1RM) Calculator

Working weight:

Use one technically consistent set of the same lift you want to plan.

Completed reps:

Use 1–10 reps when possible; 11–20 is planning-only.

Estimate strategy:

Average is balanced; median resists outliers; floor and ceiling show conservative and aggressive bounds.

Training max:

Choose 80–100%; 85–90% is a common conservative planning range.

{{ training_max_percent }}%

Load rounding:

Exact keeps full planning values; the other choices snap loads to the nearest selected-unit increment.

Display precision:

Standard shows one decimal place; precise shows two.

Formula	Estimated 1RM	Delta from selected	Copy
{{ row.label }}	{{ row.estimate }}	{{ row.delta }}

Intensity	From selected 1RM	From training max	Planning cue	Copy
{{ row.percent }}%	{{ row.estimatedLoad }}	{{ row.trainingLoad }}	{{ row.cue }}

Read agreement before load

The seven formulas span {{ formulaBand }}. {{ confidenceDetail }}

Use the training max for routine planning

The current {{ training_max_percent }}% training max is {{ trainingMaxDisplay }}. The load-plan table applies every percentage to both the selected estimate and this buffered anchor.

Keep a heavy single separate from an estimate

Match the lift, equipment, range of motion, and technique standard. Pain, fatigue, unfamiliar equipment, or uncertain spotting are reasons not to test a maximum from this number.

A hard set can answer a training question without becoming a true maximum attempt. One-repetition maximum, usually shortened to 1RM, means the greatest load completed once for a particular lift under a consistent technique standard. It is specific to the movement, equipment, range of motion, and conditions of the attempt; it is not a general score for every kind of strength.

Coaches and lifters use 1RM to turn a heavy effort into percentage-based loads. The number can anchor a training block, help compare similar sets over time, or provide a conservative training max for routine work. Direct testing is different. A real maximal single adds fatigue and requires suitable warm-up, technique, safeties, and spotting.

Tested 1RM: The heaviest single actually completed under the stated conditions.
Estimated 1RM: A projection from the weight and repetitions in a completed set.
Training max: A chosen percentage below the estimate, used to leave room for day-to-day variation.

Rep-based equations assume the set was technically consistent and demanding enough to reveal current capacity. An easy set with several repetitions still in reserve usually understates what the lifter could do, while altered range of motion or deteriorating technique can overstate a comparable max. Exercise type and muscular endurance also change how well one equation fits a person.

Uncertainty grows as the rep count rises. Research comparing repetitions-to-failure estimates has found meaningful differences among equations, especially beyond ten repetitions. Treat a low-rep estimate as a planning anchor and a high-rep estimate as broader guidance. Pain, unusual fatigue, unfamiliar equipment, or uncertain spotting are reasons not to turn any estimate into a maximal attempt.

How to Use This Tool:

Start with one honest set of the same lift you want to plan, then decide how conservatively the seven estimates should be combined.

Enter the full Working weight, choose kg or lb, and add the whole number of Completed reps. Use 1 to 10 reps when possible; 11 to 20 remains available for broad planning.
Choose an Estimate strategy. The average balances all seven formulas, the median reduces the influence of an outlying estimate, and the floor or ceiling selects the lowest or highest result.
Set the Training max from 80% to 100% and choose a practical Load rounding increment. Rounding follows the selected weight unit.
Review the selected estimate with the formula range and confidence cue before using the training-load plan. Correct any invalid weight, unit, or rep count before relying on the result.

Interpreting Results:

The selected 1RM is the chosen summary of seven equations, after any requested load rounding. Read it beside the lowest and highest formula estimates. A narrow range means the equations agree for that set; it does not prove that the estimate equals a safely testable single.

High confidence requires 5 reps or fewer and a formula spread no greater than 4% of the selected estimate.
Moderate confidence requires 8 reps or fewer and a spread no greater than 8%, unless the High conditions already apply.
Caution covers every other valid set. Use it for general programming rather than a max claim.

Technical Details:

Each equation maps working weight w and completed repetitions r to an estimated 1RM. When r equals 1, every estimate is set to the entered weight. For 2 to 20 reps, the following named equations are evaluated at full precision.

Formula Core

Equations used to estimate one-repetition maximum
Equation	Estimated 1RM
Epley	$w \times (1 + \frac{r}{30})$
Brzycki	$\frac{36 w}{37 - r}$
Lombardi	$w \times r^{0.1}$
Mayhew	$\frac{100 w}{52.2 + 41.9 e^{- 0.055 r}}$
O’Conner	$w \times (1 + 0.025 r)$
Wathan	$\frac{100 w}{48.8 + 53.8 e^{- 0.075 r}}$
Lander	$\frac{100 w}{101.3 - 2.67123 r}$

The average is the arithmetic mean of all seven estimates. The median is the middle estimate after sorting them; the conservative floor and aggressive ceiling use the minimum and maximum respectively. Formula spread is the maximum minus the minimum, and spread percentage divides that difference by the selected estimate.

A training max applies the chosen percentage to the unrounded selected estimate. Each load-plan row then multiplies either the selected estimate or the training max by 50%, 55%, and every five percentage points through 100%. If rounding is enabled, each displayed load snaps to the nearest 1, 2.5, or 5 units in kg or lb; the underlying calculations retain full precision until that display-oriented load rounding step.

Accuracy Notes:

An estimated 1RM is informational training guidance, not medical advice or a guarantee of a safe attempt. Keep the lift, technique, equipment, range of motion, and set effort comparable when tracking change. Use appropriate supervision and safeties for heavy lifting, and stop if pain or unusual symptoms occur.

References:

Muscular endurance repetitions to predict bench press strength in men of different training levels, Journal of Sports Medicine and Physical Fitness, 1995.
Evaluation of Load-Velocity Relationships and Repetitions-to-Failure Equations, Journal of Strength and Conditioning Research, 2020.