In Excel: select the cells, press Ctrl+1 ▸ Number ▸ Custom, and type a format code — for example 0.0,,"M" to show 12,400,000 as 12.4M.
On this page7
Select the cells, press Ctrl+1 (⌘1 on Mac) and choose the Number tab.
Pick the closest built-in format first — it fills the Custom box with a working code to edit.
Choose Custom and edit the code: 0 forces a digit, # hides an absent one, "text" adds literal characters.
Add a second section after a semicolon for negatives, a third for zero, a fourth for text.
Press Ctrl+1 ▸ Custom on another cell and paste the code, or use the Format Painter, to reuse it.
What this does
A number format changes how a value is DISPLAYED and never what it is: the cell still holds 12400000, so every formula that reads it still gets 12400000. A format code has up to four sections separated by semicolons — positive;negative;zero;text — and you can supply just the first, or the first two. The building blocks are 0 (a digit, padded with zero), # (a digit, blank if absent), ? (a digit, blank but aligned), a comma as thousands separator, and quotation marks around any literal text. A comma at the END of the code divides the display by a thousand, so 0.0,, shows millions. Colours go in square brackets: [Red]. And the Accounting format is not merely currency — it aligns the currency symbol at the left edge of the cell, aligns the decimal points, and shows zero as a dash, which is what makes columns of it readable. The same idea underpins a lot of everyday Excel work, so the few minutes spent getting it right here pay back across every sheet you build afterwards. Treat it as a pattern, not a one-off, and it stops being something you look up and starts being something you reach for. The difference between a quick fix and a sheet you can trust is the extra minute you spend validating “create a custom number format in excel”. Start on a copy or a tiny sample, keep the affected cells visible, and compare the result with the tool above before you touch the real workbook. When a formula is involved, keep the inputs labelled beside it, reference cells instead of typing values, and apply number formatting only after the result checks out. The point is a workspace setting that makes a big sheet comfortable to navigate, but the practical win is that someone else can open the file and understand what happened without asking you.
A worked example
Phone numbers stored as the digits 2125550147: Ctrl+1 ▸ Custom ▸ (000) 000-0000 displays (212) 555-0147 while the cell still contains the number, so sorting and lookups keep working. Revenue in millions: 0.0,,"M" turns 12400000 into 12.4M. Positive and negative in one code: #,##0;[Red](#,##0) shows 1,250 and (1,250) in red. Custom formats let one column serve both the reader and the formulas — a readable 12.4M on screen with the exact 12,400,000 still available to every calculation that touches it. If there is any chance you will reuse this, drop it into a small template tab right now: a labelled input area on the left and the formula beside it, checked once against the tool above. Next time the same question comes up, the answer is a single paste away instead of a rebuild from memory.
In Google Sheets
If you are in Google Sheets rather than Excel, the good news is that the formula shown here is identical and the workflow barely changes — menus sit across the top instead of in a ribbon, and a few function names differ slightly, but anything you build here moves across with little or no rework. The aim was to get you unstuck fast and leave you a little more capable than a copy-paste would. The answer is at the top and the detail above shows why it holds — so the next time a colleague asks, you can answer without reaching for search. If you take one thing from this page on “create a custom number format in excel”, make it the habit rather than the keystrokes: set the problem up with labelled inputs, reference those cells, and let Excel do the recomputing. Bookmark the page for the syntax, but do the example once in a blank sheet and check it against the tool above — five minutes of hands-on practice fixes the method in memory far better than re-reading, and it surfaces the small snags while they are still harmless. After that the technique is genuinely yours: faster than searching for it again, and reliable enough to drop into work that other people depend on.
Common mistakes
- Expecting a format to change the value — the cell still holds the full number, which is why a "rounded" column can still fail to add up on screen.
- Formatting phone numbers that were entered as TEXT: a number format has no effect on text, and leading zeros mean they probably are text.
- Using a custom format to hide decimals and then quoting the displayed figure as if it were exact.
- Reaching for the currency format when the column needs Accounting, which is what aligns the symbols and decimal points.
- Building a format with three commas expecting billions and getting a blank-looking cell, because each trailing comma divides by another thousand.
Frequently asked questions
How do I create a custom number format in Excel?
Select the cells, press Ctrl+1, choose Number ▸ Custom and type a format code such as #,##0.00 or 0.0,,"M".
How do I format phone numbers in Excel?
Ctrl+1 ▸ Custom ▸ (000) 000-0000 for US numbers. If the cells contain text rather than digits, convert them to numbers first or the format will do nothing.
What is the accounting number format?
A currency format that left-aligns the currency symbol at the cell edge, lines up the decimal points, and shows zero as a dash. Home ▸ Number ▸ Accounting, or Ctrl+Shift+$ for plain currency.
How do I show numbers in millions?
Use the custom code 0.0,,"M" — two trailing commas divide the display by a million, and the underlying value is unchanged.
What do the semicolons in a format code mean?
They separate up to four sections: positive;negative;zero;text. Supplying fewer sections is fine, and an empty section hides that case entirely.