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One-Rep Max Calculator
Estimates the one-repetition maximum from a weight lifted for 2–12 repetitions using the Epley, Brzycki and Lombardi equations, reports their average, and lists training loads at 95 % to 70 % of that 1RM.
When to use
You want to estimate maximal strength or program training percentages without attempting a true single-rep maximum.
Do not use when: The set was more than 12 repetitions (prediction error grows quickly) or was not taken close to failure; use a heavier, lower-rep set instead.
Formula
Epley: 1RM = w × (1 + reps/30); Brzycki: 1RM = w × 36 / (37 − reps); Lombardi: 1RM = w × reps^0.10; one_rep_max = (Epley + Brzycki + Lombardi) / 3; load_p = one_rep_max × p / 100
The equations agree within about 2 % for 2–6 reps and Epley and Brzycki coincide at 10 reps; beyond that Brzycki rises fastest and Lombardi stays lowest, so estimates diverge. Percentages use the averaged estimate.
Inputs
| Parameter | Type | Unit | Required | Description |
|---|---|---|---|---|
weight_lifted | number | kg or lb | yes | Load lifted for the set, in any unit; outputs use the same unit. Range: > 0, ≤ 2000 |
reps | integer | reps | yes | Repetitions completed with that load, ideally to (near) failure. Range: ≥ 2, ≤ 12 |
Outputs
| Output | Type | Unit | Description |
|---|---|---|---|
one_rep_max | number | Mean of the Epley, Brzycki and Lombardi estimates, in the unit of weight_lifted. | |
epley | number | 1RM = w × (1 + reps / 30). | |
brzycki | number | 1RM = w × 36 / (37 − reps). | |
lombardi | number | 1RM = w × reps^0.10. | |
percentages | list | Load at 95, 90, 85, 80, 75 and 70 % of the averaged 1RM. |
Example
100 kg × 5 reps: {"weight_lifted":100,"reps":5} → {"epley":116.7,"brzycki":112.5,"lombardi":117.5,"one_rep_max":115.5,"percentages":[{"percent":95,"load":109.8},{"percent":90,"load":104},{"percent":85,"load":98.2},{"percent":80,"load":92.4},{"percent":75,"load":86.7},{"percent":70,"load":80.9}]}
60 kg × 10 reps: {"weight_lifted":60,"reps":10} → {"epley":80,"brzycki":80,"lombardi":75.5,"one_rep_max":78.5}
GET https://tttkmbb.com/api/v1/calculate/one-rep-max?weight_lifted=100&reps=5
Machine access
- API:
GET https://tttkmbb.com/api/v1/calculate/one-rep-max(query parameters) orPOSTwith a JSON body{"inputs": {...}} - Schema: https://tttkmbb.com/api/v1/calculators/one-rep-max · Markdown: https://tttkmbb.com/fitness/one-rep-max.md · JSON definition: https://tttkmbb.com/fitness/one-rep-max.json
- MCP: server
https://tttkmbb.com/mcp, toolrun_calculator with calculator_id="one-rep-max" - OpenAPI operationId:
estimate_one_rep_max - Freshness:
static. Authentication: none. Rate limit: fair use (see rate limits).
Sources
- Reynolds JM, Gordon TJ, Robergs RA (2006) Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry, J Strength Cond Res 20:584-592 (peer_reviewed)
- Wikipedia – One-repetition maximum (formula collection with original citations: Epley 1985, Brzycki 1993, Lombardi 1989) (reference)
FAQ
Which formula is best?
For 2–6 reps they agree closely; Brzycki is widely used in the USA for bench press, Epley for squat and deadlift. Averaging reduces the influence of any one equation's bias.
Can I use pounds?
Yes. The equations are unit-free: enter pounds and every output is in pounds.
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