Field Sizes and

Field Sizesand Bookmaker Percentages

We all want to get the best 'bang' for our betting buck from the bookies. One of the key ways to achieve this is to choose the right kind of race to invest on.

As punters do we get the most value from races with small sized fields or from races where there are a lot of competitors? Bookmaker percentage or margin is the measure that tells us how much value is on offer in a particular race. The lower the bookmaker’s margin, the more value we are getting as punters. Conversely, the higher the bookie margin the poorer is the value on offer.

In races with smaller sized fields bookies have to work harder to attract the punting dollar as they get less bets from punters who follow particular horses, jockeys and stables. Many punters also chase long shot winners and often dismiss races with smaller fields as they believe that outsiders are unlikely to win. For these reasons bookmakers need to go to greater lengths to attract business to races with small field sizes. The principal way that they do this is to offer more attractive odds.

Aussieraces.comstudied every race run on metropolitan tracks in Sydney, Melbourne and Brisbane during June 2010. We looked at race field sizes relative to the amount of value offered by the bookies. The table below summarizes our findings -

                    Bookmaker Percentages Relative to Field Size*

       Number of 
         in Race





      105 -118%



      110 -123%

           9 -10


      111 -125%



      112 -128%



      114 -129%



      118 -130%



      123 -138%

( *Sample taken from all races run on metropolitan tracks in Sydney, Melbourne and Brisbane during June 2010)

The overwhelming finding of our study was quite simply this - The smaller the number of runners that are in a race, the better are the odds that are likely to be offered by the bookmakers.

The smaller the number of runners that are in a race, the better are the odds that are likely to be offered by the bookmakers”.

In reading the above table, we can see that in 5-6 horse fields bookmakers worked to an average percentage of 112% - or in other words for every $112 they took they returned $100 to the punters. At the other end of the scale in fields of 17-18 runners they weren’t nearly so generous, as for every $128 they took they returned just $100.

derbyhorseNote that in smaller sized fields bookmakers are more likely to offer better percentages, but this is not guaranteed. The percentages offered can vary greatly. For example, as the above table shows bookie percentages for fields of 5-6 runners varied between 105 and 118%.  A basic rule of thumb is that the more exposed is the form for a race, the better will be the odds offered by the bookies. Conversely, the more unknowns there are (e.g. first starters etc.) the more conservative will be the odds offered. The more conservative odds or in other words higher bookmaker margin is a kind of ' insurance' against the unknowns in the race (e.g. first starters with no official trial form which have shown ability in private trials and which may be well backed and take the bookies by surprise).

Comparing the stats, on average bookmakers are likely to offer 16% better odds in a race with 5-6 runners than they will in a race with 17-18 competitors (i.e. 112% versus 128%). This 16% margin is huge when you consider that on average professional punters in Australia look to make a 10% profit on their turnover each year.

Don’t fall for the widely held belief that you can’t get good odds in small sized fields. Indeed, many of’s winners at double figure odds have been in races with single figure runners.

Indeed, many of’s winners at double figure  
           odds have been in races with single figure runners”.

For example, in December 2009 five horses lined up in a 3 year old restricted race at Flemington. In the event was one of the shortest priced horses of the year, Rain Shadow at odds of $1.55. Every newspaper tipster in Australia selected Rain Shadow to win. However, our ratings showed that Rain Shadow was unlikely to win and selected Cabeza ($11.30) to score from Flash Madison ($9.30) with Rain Shadow third – and that’s how they finished. A $11.30 winner (rated by as the $4.00 favourite) in a five horse field where the hot favourite didn’t have much of a show – it was like shooting fish in a barrel!

Better bookie odds are not the only benefit of betting on races with smaller sized fields. Another plus is the fact that your selection is less likely to suffer interference in the run. As our recent study on luck in races showed, on average 35% of all horses have their winning chances diminished through meeting interference during the run. This is less likely to occur in smaller sized race fields. Speed maps are also easier to construct for smaller sized fields, making both the running of the race and its outcome clearer to the form analyst.


                      By Mark Hall                         Copyright