SWOLF and Stroke Index Calculator (Swimming Efficiency)
SWOLF, distance per stroke, stroke rate and Costill's stroke index from your time and stroke count for one pool length.
Results
What this tool does
SWOLF is the time for one length plus the number of strokes you took, so a lower score is better: it rewards swimming a length with fewer or faster strokes. It is only comparable at the same pool length and stroke, and it can be gamed by gliding too much, because the fastest swim is a balance of stroke rate and distance per stroke. Costill's stroke index multiplies speed by distance per stroke and is a better guide to efficiency, since it rises when you go faster without taking more strokes. Be consistent in what you count as a stroke: each arm entry, or each full left–right cycle.
Formula
SWOLF = seconds + strokes · stroke index = speed × distance per stroke (Costill)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
l | Pool length | m |
t | Time for one length | s |
k | Strokes in that length | — |
SW | SWOLF score | — |
V | Swimming speed | m/s |
DPS | Distance per stroke | m |
SR | Stroke rate | /min |
SI | Stroke index (speed × distance per stroke) | m²/s |
Worked example
- Pool length25 m
- Time for one length40 s
- Strokes in that length18
- SWOLF score58
- Swimming speed0.63 m/s
- Distance per stroke1.39 m
- Stroke rate27.0 /min
- Stroke index (speed × distance per stroke)0.87 m²/s
Limitations
- This tool is informational only. It does not diagnose, treat or replace a qualified health professional. Speak to a doctor before making decisions about your health.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.