Time Conversions

ASA Equivalent Performance Tables

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UPDATED January 2014

The current ASA Equivalent Performance Tables were computer generated by SPORTSYSTEMS. This is the official basis for all time conversions used for Championship entries by the ASA and its constituent clubs, counties and regions.

These tables are a reworked and expanded version of the original EQUIVALENT PERFORMANCE TABLES developed by Rex Smith.

Four new tables have been added to cater for the 50 metres on each of the strokes. The range of times covered by the tables has been reviewed in line with current World Records, National Standard Times and the lowest grade of the Graded Swimming system.

The tables have been determined and printed using modern computing methods, however the rules for converting times has been retained. Where differences from the original tables occur they are due to the inherently greater accuracy of the modern digital computer and to the direct transfer from computer to printers artwork.

The EQUIVALENT PERFORMANCE TABLES have been available for download from British Swimming website since 2004.

Equivalent Time Algorithm

To establish the equivalent time in a different length pool the following factors have to be allowed for:

1. Difference in distance actually covered.
2. The time benefit/deficit of executing more or less turns during the swim

The factors used have been influenced by the original manual tables.

The full process comprises:

1. Convert the actual swim time achieved to the equivalent time in a 50m pool.
2. Compute the equivalent pool time 50m pool time to the time in the desired pool length(s).

The first step process involves using the turning speed factors for the event and the difference in distance covered between the actual pool length for the swim and a 50m pool.

The second step then involves using the same turning speed factors and the new distance and pool length to convert from 50m pool length to the desired pool length.

The second step – 50m pool length to desired pool length – is expressed as:

Converted Time = T50 * PoolMeasure – TurnVal * (NumTurnperH – 1)


T50 = Time in a 50m pool

PoolMeasure = Event distance factor

TurnVal = Time per turn – The time in seconds attributed to execution of a single turn

NumTurnperH = Number of turns per 100 in the required length pool.

The Time per turn is determined by the relationship:

TurnVal = TurnFactor / T50

Where TurnFactor is provided by the LookUp table shown below.

The table also shows the PoolMeasure (Event Distance Factor) for each event in Imperial yards pools.

The PoolMeasure (Event Distance Factor) value for metric and “36 2/3y”, “27 1/2y” pools is the same constant for all events on the basis that the distance covered does not vary by very much between the two categories, i.e. 100m v 110 yds, up to 1500m v 1650 yds. (BUT note that 1650 yards is a special case)


100m Backstroke in a 50m pool in 63.5 seconds

The Time per turn is determined by the relationship:

TurnVal = TurnFactor / T50 = 40.5/63.5 = 0.63779527

For a 25m pool there is no difference in the distance swum, therefore Poolmeasure = 1 and the extra number of turns = 2.

The converted time is therefore

63.5 * 1 – 0.63779527 * 2 = 62.22 seconds

Rounded to nearest tenth and truncated = 62.2 seconds

For a 33 1/3 yds pool there is a difference in distance swum, therefore PoolMeasure = 0.91187 and the extra number of turns = 1

The converted time is therefore

63.5 * 0.91187 – 0.63779527 * 1 = 57.2659 seconds

Rounded to nearest tenth and truncated = 57.3 seconds

The first step – conversion from the actual length pool in which the swim was made to the 50m equivalent is slightly more complicated.

The expression for pool length conversion is:

Converted Time = T50 * PoolMeasure – TurnVal * (NumTurnperH – 1)

To calculate the time when converted to 50m pool length we need to solve the equation for T50.

Generalising the above equation we have:

Converted Time = T50 * PoolMeasure – (TurnFactor / T50) * (NumTurnperH – 1)

This involves solving the quadratic equation:

PoolMeasure * T50 * T50 – ActualTime * T50 – TurnFactor * (NumTurnperH – 1)

to obtain the T50 value.


100 yds Backstroke in a 25 yd pool in 56.6 seconds

For a 25 yard pool there is a difference in distance swum, therefore PoolMeasure = 0.91187 and the extra number of turns = 2

TurnFactor = 40.5 as before

NumTurnperH = 3

The quadratic to be solved is:

0.91187 * T50 * T50 – 56.6 * T50 – 40.5 * 2 = 0

So that

T50 = 63.51979

Which is consistent with our starting point for step2.


Step 1

Retrieve the Pool Length parameters for the Pool in which the time was achieved – the From Pool

1. The parameters are:

1 – “50m”, “33 1/3m”, “25m”,”20m”
2 – “36 2/3y”, “27 1/2y”
3 – “33 1/3y”, “25y”, “20y”

2. NumTurnPH – Number of turns per 100

1 – “50m”
2 – “33 1/3m”, “36 2/3y”, “33 1/3y”
3 – “25m”, “27 1/2y”, “25y”
4 – “20m”, “20y”

Step 2

Check for recognised pool length – (PoolMeasFlag <> 0 and NumTurnPH <> 0)

Step 3

Check that the event stroke and distance is consistent with the From Pool length

Step 4

Check that the Time field contains a valid time and get numeric seconds from user input text

Step 5

If actual time achieved was not in a 50m pool then convert the time to the 50m pool equivalent.

The following parameters are required:

PoolMeasure – Factor to allow for distance covered

Case 1 Pool Length – “50m”, “33 1/3m”, “25m”,”20m” PoolMeasure = 1

Case 2 Pool Length – “36 2/3y”, “27 1/2y” PoolMeasure = 1.006041

Case 3 Pool Length – “33 1/3y”, “25y”, “20y” PoolMeasure from table below

TurnFactor – Factor to determine time per turn

NumbTurn – Number of extra turns per 100

Distance – 50,100,200,400,800,1500 except when 1650 yards in a 25 yard pool

50 Free0.9114742.245
100 Free0.9108742.245
200 Free0.9115743.786
400 Free0.9119744.233
800 Free0.9121745.525
1500 Free1.00415546.221
50 Breast0.9114763.616
100 Breast0.9089563.616
200 Breast0.9109766.598
50 Fly0.9114738.269
100 Fly0.9109738.269
200 Fly0.9117739.76
50 Back0.9114740.5
100 Back0.9118740.5
200 Back0.9124741.98
200 IM0.9044349.7
400 IM0.9104655.366

TimeTo50 = (swtime + Sqr(swtime * swtime + 4 * PoolMeasure * TurnFactor * NumbTurn)) / (2 * PoolMeasure)

Step 6

Convert time in 50m. to equivalent time in the required pool length

1. Retrieve the Pool Length parameters for the Pool to which the time is to be converted- the To Pool
2. Retrieve the turn and distance correction factors for the new pool length

Convert turn factor to a time per turn

3. TurnVal = TurnFactor / Timeval * (Distance / 100)

Check for special case of 1500 in Yards pool

DistImp = Distance
If Evntcode = 6 And PoolMeasFlag = 3 Then
DistImp = 1650
End If

The following conversions are not catered for:

  • 1650 yards in a 2 or 4 turns/100 pool
  • 200 I.M. in 2 or 4 turns/100 pool
  • 50 any stroke in a 2 or 4 turns/100 pool

Do the conversion

Allowance for different distance covered

DistTime = Timeval * PoolMeasure

Allowance for extra turns

TurnTime = TurnVal * (DistImp / 100) * (NumTurnPH – 1)

Round to nearest tenth

ConvTime = DistTime – TurnTime + 0.05

The time has been rounded to nearest tenth so truncate to prevent display of the hundredths. Convert to alpha format and express as MM:SS.T