# Swim Pace Calculator

> Computes swimming pace per 100 metres and per 100 yards, speed in m/s and km/h, and the number of 25 m and 50 m pool lengths from a swum distance and time.

- Calculator id: `swim-pace` · Category: Sports & Fitness (`fitness`) · Tool name: `calculate_swim_pace`
- Canonical page: https://tttkmbb.com/fitness/swim-pace · This document: https://tttkmbb.com/fitness/swim-pace.md · JSON definition: https://tttkmbb.com/fitness/swim-pace.json

## Purpose

Computes swimming pace per 100 metres and per 100 yards, speed in m/s and km/h, and the number of 25 m and 50 m pool lengths from a swum distance and time.

**Use when:** You swam (or plan to swim) a given distance in a given time and need the pace per 100 m or 100 yd, e.g. to set interval targets.

**Do not use when:** The distance is in yards (convert first: 1 yd = 0.9144 m) or you need running/cycling pace (use running-pace or pace-converter).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `distance_m` | number | m | required | Distance swum in metres. (> 0, max 100000) |
| `time` | string |  | required | Elapsed time as h:mm:ss, mm:ss (30:00) or plain minutes. |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `pace_per_100m` | string | min:sec/100 m | Time per 100 metres. |
| `pace_per_100yd` | string | min:sec/100 yd | Time per 100 yards (91.44 m). |
| `pace_seconds_per_100m` | number | s/100 m | Same pace as seconds per 100 m. |
| `speed_m_per_s` | number | m/s | Average speed in metres per second. |
| `speed_kmh` | number | km/h | Average speed in kilometres per hour. |
| `lengths_25m_pool` | number | lengths | distance_m / 25. |
| `lengths_50m_pool` | number | lengths | distance_m / 50. |

## Formula

`pace_100m = time_seconds × 100 / distance_m; pace_100yd = pace_100m × 0.9144; speed_m_per_s = distance_m / time_seconds; speed_kmh = speed_m_per_s × 3.6`

## Data Sources

- NIST Special Publication 811 – Guide for the Use of the SI (Appendix B: 1 mile = 1609.344 m, 1 yard = 0.9144 m) — https://www.nist.gov/pml/special-publication-811 (standard, retrieved 2026-09-23)
- World Aquatics – Facilities Rules (25 m and 50 m competition pools) — https://www.worldaquatics.com/rules (standard, retrieved 2026-09-23)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/swim-pace?distance_m=…&time=…`
- `POST https://tttkmbb.com/api/v1/calculate/swim-pace` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/swim-pace · OpenAPI operationId `calculate_swim_pace` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "swim-pace", "inputs": {…}}`

## Example

- 1500 m in 30:00: inputs `{"distance_m":1500,"time":"30:00"}` → `{"pace_per_100m":"2:00","pace_per_100yd":"1:50","pace_seconds_per_100m":120,"speed_m_per_s":0.833,"speed_kmh":3,"lengths_25m_pool":60}`
- 400 m in 6:40: inputs `{"distance_m":400,"time":"6:40"}` → `{"pace_per_100m":"1:40","pace_per_100yd":"1:31","speed_m_per_s":1,"speed_kmh":3.6,"lengths_50m_pool":8}`

```
GET https://tttkmbb.com/api/v1/calculate/swim-pace?distance_m=1500&time=30%3A00
```

## Limitations

The distance is in yards (convert first: 1 yd = 0.9144 m) or you need running/cycling pace (use running-pace or pace-converter). All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why is the pace per 100 yards faster than per 100 metres?**

100 yards is 91.44 m, about 8.6 % shorter, so the same speed gives a proportionally shorter time. Short-course-yards (SCY) times are not directly comparable with metres.

**What is a typical pace?**

Recreational lap swimmers commonly hold 2:00–2:30 per 100 m; competitive distance swimmers are near 1:05–1:15 per 100 m.

## Related

- [Pace Converter](https://tttkmbb.com/fitness/pace-converter.md) — Convert running paces and speeds between units.
- [Calories Burned Calculator](https://tttkmbb.com/fitness/calories-burned.md) — Energy cost of the swim from its duration.