Stackable items are items that only take up one space in a player's inventory not being carried in note form. When multiple stackable items are carried in the inventory, a number is shown on the item's picture to indicate the quantity of items in the stack. Most items stored in the bank will stack, even if they don't stack in a player's inventory. A few exceptions would be brawling gloves, satchels, and the various forms of the morphic tool. Stackable items do not weigh anything, and cannot be withdrawn from the bank as a note.
The maximum number of an item that a player can hold in a stack is 2,147,483,647, as limited by a signed (positive and negative) 32-bit integer, i.e. 231 - 1.
Jagex would only be able to expand this if 64-bit integers were used instead, as unsigned (positive only) integers do not exist as a primitive data type in Java. This would be problematic to implement, however, as it would require doubling the amount of storage space used for all item quantities. Using longs would enable up to 9,223,372,036,854,775,807 items in a stack.
It should also be noted that a player can own more than this amount of gold, but can only hold that many in a single stack. For instance, a player could hold 2,147,483,647 in an inventory and another 2,147,483,647 in his bank, so long as the two stacks are never combined.
In a question and answer session with Andrew Gower, he stated that Jagex wouldn't switch to longs because there are too many lines of code to change.
If the value of items displayed in the Price Checker window exceeds the value, then all that will be displayed is '----'.
When referring to numbers, truncation is the removal of less significant digits from the end of a number. In RuneScape, stacks of items have their quantity truncated to reduce the number of characters required to show the quantity of an item in a stack.
For stacks of items containing less than 100,000, the amount is rendered precisely, such as "31633", and the examine text is that of an individual item. For stacks of 100,000 or more, the examine text displays the exact number of items in the stack. The following conventions are used to display the quantity in a bank or inventory slot: