# Rowing Split Calculator

> Converts an indoor-rowing distance and time (or a 500 m split) into the split per 500 m, pace per km, speed, power in watts using Concept2's watts = 2.80 / pace³ and the Performance Monitor's calorie rate, weight-adjusted when body weight is given.

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

## Purpose

Converts an indoor-rowing distance and time (or a 500 m split) into the split per 500 m, pace per km, speed, power in watts using Concept2's watts = 2.80 / pace³ and the Performance Monitor's calorie rate, weight-adjusted when body weight is given.

**Use when:** You want the split, watts or calories for an erg piece, need to convert a target split into watts (or a wattage into a split) or want the finish time for a distance at a given split.

**Do not use when:** You are rowing on water (boat speed depends on hull and crew, and no watts are displayed) or you need running or swimming pace (use running-pace or swim-pace).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `distance_m` | number | m | optional | Distance rowed in metres (e.g. 2000). Give it with time, or with split_per_500m to get the finish time. (> 0, max 1000000) |
| `time` | string |  | optional | Elapsed time for distance_m as h:mm:ss, mm:ss (8:00) or plain minutes. |
| `split_per_500m` | string |  | optional | Pace per 500 m as m:ss or m:ss.s (2:00.5); used when distance_m and time are not both given. |
| `weight_kg` | number | kg | optional | Optional rower weight for the weight-adjusted calorie rate (the monitor assumes 79.5 kg / 175 lb). (> 0, max 300) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `split_per_500m` | string | m:ss.s/500 m | Time per 500 metres, as shown on the monitor. |
| `split_seconds_per_500m` | number | s/500 m | Same split as a number of seconds. |
| `watts` | number | W | Concept2: watts = 2.80 / (split_seconds / 500)³. |
| `pace_per_km` | string | min:sec/km | Time per kilometre (2 × split). |
| `speed_m_per_s` | number | m/s | 500 / split_seconds. |
| `speed_kmh` | number | km/h | Same speed in km/h. |
| `calories_per_hour` | number | kcal/h | Performance Monitor rate 4 × watts × 0.8604 + 300, with 300 replaced by 1.714 × weight_lb when weight_kg is given. |
| `time` | string | h:mm:ss | Elapsed time for distance_m (given or computed from the split). |
| `distance_m` | number | m | Distance of the piece, when given. |
| `calories_kcal` | number | kcal | calories_per_hour × time / 3600 (only when the duration is known). |

## Formula

`split_s = time_s × 500 / distance_m (or time_s = split_s × distance_m / 500); pace = split_s / 500 (s/m); watts = 2.80 / pace³; speed = 500 / split_s; calories_per_hour = 4 × watts × 0.8604 + 300 (monitor, 175 lb rower) or 4 × watts × 0.8604 + 1.714 × weight_lb (weight-adjusted); calories = calories_per_hour × time_s / 3600`

watts = 2.80/pace³ and the weight correction (true kcal/h = monitor kcal/h − 300 + 1.714 × weight in lb) are Concept2's published formulas. The monitor's rate itself follows from 25 % mechanical efficiency (× 4) and 1 W = 0.8604 kcal/h (3600/4184) plus a 300 kcal/h base for a 79.5 kg rower; it is an estimate, not a measurement.

## Data Sources

- Concept2 – Watts Calculator (watts = 2.80 / pace³, pace in seconds per metre) — https://www.concept2.com/indoor-rowers/training/calculators/watts-calculator (reference, retrieved 2026-09-24)
- Concept2 – Calorie Calculator (Performance Monitor calories are based on a 175 lb / 79.5 kg rower; correction 1.714 × weight in lb) — https://www.concept2.com/indoor-rowers/training/calculators/calorie-calculator (reference, retrieved 2026-09-24)

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/rowing-split?`
- `POST https://tttkmbb.com/api/v1/calculate/rowing-split` 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/rowing-split · OpenAPI operationId `calculate_rowing_split` 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": "rowing-split", "inputs": {…}}`

## Example

- 2000 m in 8:00: inputs `{"distance_m":2000,"time":"8:00"}` → `{"split_per_500m":"2:00.0","split_seconds_per_500m":120,"watts":202.5,"pace_per_km":"4:00","speed_m_per_s":4.167,"speed_kmh":15,"calories_per_hour":997,"time":"0:08:00","calories_kcal":133}`
- 2:30 split, 90 kg rower: inputs `{"split_per_500m":"2:30","weight_kg":90}` → `{"split_seconds_per_500m":150,"watts":103.7,"pace_per_km":"5:00","speed_kmh":12,"calories_per_hour":697}`

```
GET https://tttkmbb.com/api/v1/calculate/rowing-split?distance_m=2000&time=8%3A00
```

## Limitations

You are rowing on water (boat speed depends on hull and crew, and no watts are displayed) or you need running or swimming pace (use running-pace or swim-pace). watts = 2.80/pace³ and the weight correction (true kcal/h = monitor kcal/h − 300 + 1.714 × weight in lb) are Concept2's published formulas. The monitor's rate itself follows from 25 % mechanical efficiency (× 4) and 1 W = 0.8604 kcal/h (3600/4184) plus a 300 kcal/h base for a 79.5 kg rower; it is an estimate, not a measurement. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**How do I convert watts back to a split?**

split_seconds = 500 × (2.80 / watts)^(1/3). For example 200 W gives 120.5 s, a 2:00.5 split.

**Why does halving the split not double the watts?**

Power rises with the cube of speed: going from 2:00 to 1:50 (9 % faster) needs about 30 % more watts (202 → 263 W).

**Are the calories accurate?**

They are the monitor's estimate for a 79.5 kg rower; with weight_kg the base rate is scaled by weight. Individual efficiency varies, so treat ±15 % as normal.

## Related

- [Calories Burned Calculator](https://tttkmbb.com/fitness/calories-burned.md) — MET-based energy estimate for rowing at a fixed intensity.
- [Swim Pace Calculator](https://tttkmbb.com/fitness/swim-pace.md) — Pace per 100 m for swimming pieces.
- [Power Converter](https://tttkmbb.com/conversion/power.md) — Convert watts to other power units.