# Cycling and swimming pace calculator

> Cycling power-to-weight (W/kg), speed and pace, or swimming pace per 100 m and 100 yd with your SWOLF score.

Interactive version: https://www.calcopenly.com/health/cycling-swimming-pace-calculator
Subject: Health and fitness calculators

For cycling, power-to-weight is power in watts divided by body weight in kilograms (W/kg), and speed converts to pace as 3,600 ÷ km/h seconds per kilometre, with the time for a chosen ride distance. For swimming, pace is time ÷ distance × 100, per 100 m and per 100 yd, and SWOLF adds the average strokes per length to the average seconds per length.

Cyclists compare W/kg because it sets climbing speed, and swimmers track SWOLF as a measure of efficiency. A 75 kg rider holding 250 W has 3.33 W/kg, and at 30 km/h a 40 km ride takes 1:20:00. A swimmer covering 400 m in 8:00 in a 25 m pool swims 2:00 per 100 m and, at 18 strokes per length, scores a SWOLF of 48.

W/kg ignores aerodynamic drag, which dominates on flat roads. SWOLF scores are comparable only within the same pool length and stroke-counting method.

## Inputs

- **Sport** (options: Cycling, Swimming)
- **Power (FTP or ride average)**
- **Body weight**
- **I know my** (options: Speed, Pace)
- **Speed**
- **Pace per km**: mm:ss
- **Ride distance**
- **Swim distance**
- **Swim time**: mm:ss or h:mm:ss
- **Pool length**
- **Strokes per length (average)**: Garmin counts one stroke per full cycle of the arm wearing the watch

## Results

- Pace — main result
- Pace per mile (per mile)
- Pace per 100 yd (per 100 yd)
- Speed (km/h)
- Speed in miles per hour (mph)
- Power-to-weight (W/kg)
- Power-to-weight per pound (W/lb)
- Time for the ride distance
- SWOLF (strokes + seconds per length)
- Lengths swum

## Formula

$$
\frac{P}{m}\ \text{(W/kg)},\qquad \text{pace} = \frac{3600}{v_{\text{km/h}}}\ \text{s/km},\qquad \text{SWOLF} = \text{strokes} + \text{seconds per length}
$$

## Worked examples

### 250 W at 75 kg, 30 km/h for 40 km

- Sport: Cycling
- Power (FTP or ride average): 250 W
- Body weight: 75 kg
- I know my: Speed
- Speed: 30 km/h
- Ride distance: 40 km
- **Power-to-weight: 3.33 W/kg**
- **Power-to-weight per pound: 1.51 W/lb**
- **Pace: 2 min**
- **Pace per mile: 3 min 13 s**
- **Time for the ride distance: 1 h 20 min**
- Checked against: Python 3.8 decimal: 250/75; 250/(75/0.45359237); 3600/30 s/km; 40/30 h

### Bike pace 2:30 per km to speed

- Sport: Cycling
- Power (FTP or ride average): 250 W
- Body weight: 75 kg
- I know my: Pace
- Pace per km: 2:30
- Ride distance: 40 km
- **Speed: 24.00 km/h**
- **Pace: 2 min 30 s**
- Checked against: 3600 s/h ÷ 150 s/km = 24 km/h

### 400 m in 8:00, 25 m pool, 18 strokes

- Sport: Swimming
- Swim distance: 400 m
- Swim time: 8:00
- Pool length: 25 m
- Strokes per length (average): 18
- **Pace: 2 min**
- **Pace per 100 yd: 1 min 49 s**
- **Lengths swum: 16**
- **SWOLF (strokes + seconds per length): 48.0**
- Checked against: Python 3.8 decimal: 480 s/4 = 120 s per 100 m; × 0.9144 per 100 yd; 18 + 480/16

### Yard pool: 500 yd in 7:30, 15 strokes

- Sport: Swimming
- Swim distance: 500 yd
- Swim time: 7:30
- Pool length: 25 yd
- Strokes per length (average): 15
- **Pace per 100 yd: 1 min 30 s**
- **Pace: 1 min 38 s**
- **Lengths swum: 20**
- **SWOLF (strokes + seconds per length): 37.5**
- Checked against: Python 3.8 decimal: 450 s/5 = 90 s per 100 yd; 450/457.2 m × 100 = 98.4252 s per 100 m; 15 + 450/20

### Garmin's example: 15 strokes, 30 s per length

- Sport: Swimming
- Swim distance: 100 m
- Swim time: 2:00
- Pool length: 25 m
- Strokes per length (average): 15
- **SWOLF (strokes + seconds per length): 45.0**
- **Pace: 2 min**
- Checked against: Garmin Swim 2 manual: 30 seconds plus 15 strokes equals a SWOLF of 45

### Edge: 300 W rider weighing 200 lb

- Sport: Cycling
- Power (FTP or ride average): 300 W
- Body weight: 200 lb
- I know my: Speed
- Speed: 30 km/h
- Ride distance: 40 km
- **Power-to-weight: 3.31 W/kg**
- **Power-to-weight per pound: 1.50 W/lb**
- Checked against: Python 3.8 decimal: 300/(200 × 0.45359237) = 3.30693; 300/200 = 1.5 W/lb

## Questions

### How do you calculate watts per kilogram?

Divide power in watts by body weight in kilograms. A 75 kg rider producing 250 W has 250 ÷ 75 = 3.33 W/kg, or 1.51 W/lb at 165 lb. Riders usually quote W/kg at functional threshold power (FTP), which Allen and Coggan describe as the highest power sustainable for about an hour and estimate as 95 % of the average from a 20-minute test.

### What is SWOLF in swimming?

SWOLF, from swim and golf, is the number of strokes plus the number of seconds for one pool length, and as in golf a lower score is better. Garmin's example is 15 strokes in 30 seconds, a score of 45. Because it depends on pool length and on how strokes are counted (Garmin counts one per full cycle of the watch arm), scores are comparable only for the same pool and device.

### How do you convert cycling speed to pace?

Divide 3,600 by the speed in km/h to get seconds per kilometre: 30 km/h is 120 s, or 2:00 per km, and 24 km/h is 2:30 per km. For pace per mile, divide 5,793.6 by the speed in km/h, because a mile is exactly 1.609344 km: 30 km/h is 3:13 per mile.

### How do you convert swim pace per 100 m to per 100 yd?

Multiply by 0.9144, because 100 yd is exactly 91.44 m. A pace of 2:00 per 100 m (120 s) becomes 109.7 s, about 1:50 per 100 yd. Going the other way, divide by 0.9144, so 1:30 per 100 yd is about 1:38 per 100 m. The yard is defined as 0.9144 m exactly (NIST SP 811).

### How accurate is the cycling and swimming pace calculator?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 6 worked examples whose answers come from independent sources; for example, “250 W at 75 kg, 30 km/h for 40 km” is checked against Python 3.8 decimal: 250/75; 250/(75/0.45359237); 3600/30 s/km; 40/30 h.

### Where does the method come from?

Allen H, Coggan A. Training and Racing with a Power Meter, 3rd ed. VeloPress; 2019 — power-to-weight (W/kg); Garmin Swim 2 owner's manual — swim terminology (SWOLF); NIST SP 811 — 1 yd = 0.9144 m, 1 mi = 1609.344 m exactly.

## Sources

- Allen H, Coggan A. Training and Racing with a Power Meter, 3rd ed. VeloPress; 2019 — power-to-weight (W/kg)
- [Garmin Swim 2 owner's manual — swim terminology (SWOLF)](https://www8.garmin.com/manuals/webhelp/garminswim2/EN-US/GUID-9481691E-B9E0-4793-BDF7-4F78D8703E2B.html)
- [NIST SP 811 — 1 yd = 0.9144 m, 1 mi = 1609.344 m exactly](https://www.nist.gov/pml/special-publication-811)