Solid Serial Number Banknotes - What Are They and How Rare Are They?

When it comes to collectible banknotes, the term "solid serial" describes the serial number on a note where all the digits are the same.

For example, a banknote with the serial number 888888 or 777777 would be considered a solid serial note.

The solid serial number does not need to include the prefix (for example AH/01), but just describes the numbers after the prefix.

Solid serial numbers are highly prized by collectors for their incredible rarity realtive to normal notes and their "cool factor". 

How Rare is A Solid Serial Number Banknote?

The exact rarity of each solid serial number note depends on the number of digits in the serial number.

Up until 2016, most circulating Australian banknotes had 6 digits in the serial number, which means there were a million notes printed with each prefix.

For notes like that, there can be a mazimum of 9 solid serial numbers in a print run of any single prefix: 111111; 222222; 333333; 444444; 555555; 666666; 777777; 888888 and 999999. 

This means that, at the very most, just 0.0009% notes in any print run will have a solid serial number. 9 notes in a million is a ratio of 111,111 to 1.

That is an exponential increase in rarity over the standard notes that a solid serial is taken from!

Australian banknotes issued from 2016 under the NGB banknote series have 7 digits in each serial number, so notes from the NGB series with solid serial numbers are ten times rarer than those printed before 2016.

9 notes in ten million is an incredible ratio of 1,111,111 to 1.

When we keep in mind that many print runs of banknotes do not run to the full million in each prefix, their rarity relative to standard notes is increased again.

When we consider that most of the notes in any print run are used, withdrawn and destroyed, their availability to collectors in any condition years or decades after they were released is almost mind-boggling.

Every banknote collector knows that a note in mint condition is far rarer and therefore more valuable than the same note in circulated condition, so the apex of collecting solid number notes is to obtain them in mint / Uncirculated condition.

Many collectors can go their entire career without having the opportunity to see or buy one solid serial number note in any condition, much less one in perfect "mint" condition.