Excel Unplugged

15 digit limit in Excel

15 digit limit in Excel is something everyone should know about. Why? It both enables Excel to do lightning speed calculations and limits Excel in a great way. And the guilty party is IEEE 754.

15 digit limit in excel

Whenever you work with large files in Excel, so many worksheets with countless formulas, you have probably wondered, how does Excel do it so fast… Well if it wasn’t for IEEE 754, it would take an eternity. But this cutting of corners or rather of numbers also has a downside. But first things first. What is IEEE 754?

What is IEEE 754 and why can it give you a heart attack in Excel

“Microsoft Excel was designed around the IEEE 754 specification with respect to storing and calculating floating-point numbers. IEEE is the Institute of Electrical and Electronics Engineers, an international body that, among other things, determines standards for computer software and hardware. The 754 specification is a very widely adopted specification that describes how floating-point numbers should be stored in a binary computer. It is popular because it allows floating-point numbers to be stored in a reasonable amount of space and calculations to occur relatively quickly. The 754 standard is used in the floating-point units and numeric data processors of nearly all of today’s PC-based microprocessors that implement floating-point math, including the Intel, Motorola, Sun, and MIPS processors.” (Direct quote from http://support.microsoft.com/kb/78113)

What it all means

You will notice this standard in many ways in Excel, but the main is, that if you write an integer with more than 15 digits (which is quite feasible), excel will transform all integers starting with the 16th to zero.

So when you put 1234567890123456789 in a cell, you get 1234567890123450000. The same goes for 1234567890.123456789 that would give 1234567890.123450000! This is by itself quite a drawback, but it doesn’t end there, this limitation impacts all parts of Excel, including calculations. Below is a very simple calculation…15 digit limit in excel

Adding the three numbers in A1, A2 and A3 should result in 0, but you get something else entirely different. This is due to another limitation that is a side effect of the IEEE 754. More precisely, it is a side effect of something that excel did not adopt from IEEE 754 and that is the “negative zero”. So when excel should give something like -0.x as a side result or as the end result, you are in trouble. One daring bystander could even say Excel doesn’t really calculate correctly!

Is there a way around this

The short answer is NO. The long answer is, you can store longer number as text (so begin writing in Excel with an apostrophe), and you will see more than 15 integers, but if you will want to convert them back to numbers and do calculations with them, you will again only work with 15 integers!

The only way to make Excel more precise, is by using an Add-In. There are many out there, here is an example: xlPrecision

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