SWOLF Analyzer

Course preset:

The preset synchronizes the pool length and unit without changing lap entries.

Pool length:

Use 10–100 meters or yards. Custom lengths are valid when every row covers that same length.

Lap entries:

Use time,strokes, such as 25.8,21 or Lap 6,1:05.4,48. Keep the same stroke style and counting convention.

Reference block:

Opening blocks are useful for fade checks; whole-set average shows deviation around the complete effort.

SWOLF drift alert:

{{ formatNumber(drift_threshold_pct, 0) }}%

Use 2–12%. This is a review threshold, not a universal performance standard.

Rest deduction:

Leave at 0 unless every imported split includes the same measured rest interval.

s per lap

Set segments:

Short sets may produce fewer non-empty blocks than the selected maximum.

Display precision:

Choose one or two decimal places for displayed metrics.

Measure	Current set	Review note	Copy
{{ row.label }}	{{ row.value }}	{{ row.note }}

Which laps changed SWOLF, and did split time, stroke count, or both drive the change?

Lap	Split	Strokes	SWOLF	Delta	Driver call	Copy
{{ row.label }}	{{ formatSeconds(row.adjusted_split_s) }}	{{ formatNumber(row.strokes) }}	{{ formatNumber(row.swolf) }}	{{ formatSigned(row.swolf_delta) }}	{{ row.driver_label }}

Segment	Laps	Avg split	Avg strokes	Avg SWOLF	Vs opening	Copy
{{ row.label }}	{{ row.lap_range }}	{{ formatSeconds(row.average_split_s) }}	{{ formatNumber(row.average_strokes) }}	{{ formatNumber(row.average_swolf) }}	{{ formatSigned(row.delta_vs_opening_swolf) }}

Pool swimmers often trade speed for stroke count. Taking fewer strokes can save effort but may slow the split, while a faster split can require more strokes. SWOLF combines both into one number for a single pool length by adding elapsed seconds and stroke count. A 25-second length with 11 strokes therefore has a SWOLF of 36.

The score is most useful as a repeatable personal comparison. Pool length changes the time portion, stroke style changes the movement pattern, and devices may count one arm or both arms differently. Raw SWOLF should not be compared across different course lengths, strokes, counting conventions, drill types, or swimmers as if it were a universal rating.

A lower score can come from a faster split, fewer strokes, or both.
A higher score can reflect fatigue, a deliberate technique change, traffic, a turn problem, or a harder pacing choice.
A steady score can hide one input rising while the other falls, so time and stroke count should remain visible.
An opening reference is useful for fade checks; a whole-set reference shows variation around the complete effort.

Set shape matters more than one isolated lap. Comparing ordered segments can reveal a late rise in time, strokes, or both. Variation and trend add another view: coefficient of variation describes relative spread around the average SWOLF, while a per-lap slope describes the direction of change across the set.

SWOLF is not a complete measure of swimming efficiency. Starts, turns, underwater distance, rest, pacing purpose, stroke quality, and fatigue can change the score or its meaning. Use it with split times, stroke counts, technique notes, and the intent of the set.

How to Use This Tool:

Keep every row comparable, then choose the reference block that matches the training question.

Select the Course preset or set a custom Pool length from 10 to 100 meters or yards, then enter one Lap entry per line as split time and stroke count. Each row must cover one length of the same course.
Choose Reference block. Use an opening block to study fade, or the whole-set average to inspect deviations around the complete set.
Set the SWOLF drift alert from 2% to 12%. This is a personal review boundary, not a universal performance standard.
Use Rest deduction only when every split includes the same measured wall pause. Review the set call, lap drivers, and segment changes together before judging the score.

Interpreting Results:

Average SWOLF summarizes the entered set, while the selected reference controls every lap delta. A lap at or above the positive drift threshold is marked above reference. A lap at or below the negative threshold is marked improved. Values between those inclusive edges remain within the drift band.

Check the driver call to see whether a change came from split time, stroke count, or both.
The opening-to-closing call uses segment averages. A positive shift at the threshold or higher is a late fade; a negative shift at the threshold or lower is a stronger finish.
Compare repeated sets only when course, stroke, counting convention, reference choice, rest treatment, and set purpose remain consistent.

Technical Details:

Each accepted row contains one positive split of no more than 60 minutes and one positive stroke count of no more than 200. Minute-second and hour-minute-second time forms are converted to seconds. A uniform rest deduction is subtracted before SWOLF, pace, reference, segment, and trend calculations.

Formula Core:

SWOLF is calculated per length. Reference drift and consistency measures use the same full-precision lap scores.

\begin{array}{lcl} t_{adjusted} & = & t_{recorded} - t_{rest} \\ W_{i} & = & t_{i, adjusted} + s_{i} \\ d_{i} & = & \frac{W_{i} - {\bar{W}}_{ref}}{{\bar{W}}_{ref}} \times 100 % \\ CV & = & \frac{σ_{W}}{\bar{W}} \times 100 % \end{array}

W is SWOLF, t is time in seconds, s is stroke count, and d is drift from the selected reference average. Coefficient of variation uses population standard deviation. Display precision of one or two decimals affects presentation only.

Pace per 100 course units equals total adjusted time divided by entered distance, multiplied by 100. Meter-normalized pace converts each yard to 0.9144 meters before applying the same rule. The SWOLF slope is the ordinary least-squares slope of full-precision lap scores against one-based lap number, reported as score per lap.

Rule Core:

SWOLF reference, drift, and segment rules
Decision	Exact behavior
Reference rows	First 2; first 3; first ceiling(n/3); or every entered lap.
Lap status	Improved at drift ≤ −threshold; above reference at drift ≥ threshold; otherwise within threshold.
Segments	Split chronological rows into up to 2, 3, or 4 non-empty blocks using proportional integer boundaries.
Set call	Compare closing-segment average with opening-segment average as a percentage; apply the same inclusive drift threshold.

A rest deduction must be smaller than every recorded split. The source accepts at most 200 lap rows and 50,000 characters. Short sets may produce fewer segments than requested because empty blocks are not created.

Limitations:

Lap entries are analyzed in the current browser. SWOLF remains a training descriptor rather than a universal efficiency score.

Do not compare raw scores across pool lengths, stroke styles, devices, or stroke-count conventions.
A uniform rest deduction is valid only when the same measured pause is included in every split.
Use technique observation, set purpose, and fatigue context before treating a rising score as a problem.

References:

Swim Terminology, Garmin.
Swimming metrics, Polar.