One-Rep-Max & Plate Loader

1RM from any set (7 formulas + average), % and RPE tables, and which plates to load.

Weight lifted (required)

Repetitions (required)

Reps completed in the set. Estimates are most reliable up to about 10 reps.

Unit

RPE of the set

Optional (6–10). 10 = to failure; 8 = two more reps were possible. Reps in reserve are added before estimating.

Weight to load

Optional total bar weight for the plate loader.

Or: percentage of 1RM to load %

Used when no weight to load is given; default 100% of the average estimate.

Bar weight

Default 20 kg or 45 lb.

Collars (both together)

Plates available

Plate weight and how many you have in total (both sides). Empty = a standard set (kg: 25–1.25, lb: 45–2.5).

Plates available
#	Plate weight	Count
1
2
3
4

Try an example: 100 kg × 5 reps, load 85% · 225 lb × 8 at RPE 8, load 275 lb · Home gym: 62.5 kg with a 15 kg bar and few plates

How it works

Estimates your one-repetition maximum from the weight and reps of a set to failure (or with an RPE) with the Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner and Wathan equations and their average, prints a percentage table and an RPE table, and tells you which plates to put on each side of a kg or lb bar using only the plates you actually have.

Seven published equations estimate the 1RM from the weight w and repetitions r to failure, as tabulated by LeSuer et al. (1997): Epley w(1 + 0.0333r); Brzycki 100w/(102.78 − 2.78r); Lander 100w/(101.3 − 2.67123r); Lombardi w·r^0.10; Mayhew 100w/(52.2 + 41.9e^(−0.055r)); O'Conner w(1 + 0.025r); Wathan 100w/(48.8 + 53.8e^(−0.075r)). The average of all seven is the headline estimate.
With 1 rep (and no RPE) the 1RM is the weight lifted.
RPE: reps in reserve = 10 − RPE are added to the reps (e.g. 5 reps at RPE 8 count as 7 reps to failure). The RPE table uses the same idea with the Epley relation %1RM = 1 ÷ (1 + 0.0333 × (reps + 10 − RPE)); it is derived, not a copy of a published RPE chart.
Percentage table: weight = % × average 1RM; the approximate reps at each percentage invert the Epley equation: reps = (1/% − 1) ÷ 0.0333.
Plate loader: per side = (target − bar − collars) ÷ 2. Plates are taken heaviest first (greedy) from the pairs you have; if that misses but an exact combination exists (possible with unusual plate sets), an exact subset-sum search finds the combination with the fewest plates. If the weight cannot be loaded exactly, the nearest loadable weights below and above are shown.

Sources

LeSuer, McCormick, Mayhew, Wasserstein & Arnold (1997). The Accuracy of Prediction Equations for Estimating 1-RM Performance in the Bench Press, Squat, and Deadlift. J Strength Cond Res 11(4): 211–213 (National Strength and Conditioning Association)

For scripts and AI agents

JSON API: POST https://onerepmaxcalculator.usefulweb.site/api/v1/calculate (same calculation as this page)
Interface description: OpenAPI 3.1 · AI guide: llms.txt
MCP server (Streamable HTTP): https://onerepmaxcalculator.usefulweb.site/mcp · tool name one_rep_max_calculator

Example request

curl -s -X POST https://onerepmaxcalculator.usefulweb.site/api/v1/calculate \
  -H 'content-type: application/json' \
  -d '{"weight":100,"reps":5,"unit":"kg","targetPercent":85}'