Please Note: This article is written for users of the following Microsoft Excel versions: 2007, 2010, 2013, 2016, 2019, and Excel in Office 365. If you are using an earlier version (Excel 2003 or earlier), this tip may not work for you. For a version of this tip written specifically for earlier versions of Excel, click here: Developing Reciprocal Conversion Formulas.

Developing Reciprocal Conversion Formulas

by Allen Wyatt
(last updated January 1, 2022)

3

Jeremy posed a problem that is based on two cells, A1 and C1. These cells are designed to contain inches and millimeters, respectively. Jeremy wants a way that someone could enter a value in A1 and it would be converted to millimeters in C1. Conversely, they could enter a value in C1 and it would be converted to inches in A1.

Doing the conversion, of course, isn't the real issue. The problem is that if someone enters a value in A1, that value will overwrite any formula that may be in that cell, and mean that any subsequent value entered in cell C1 would not give the required conversion in the previously overwritten A1.

There are a couple of different ways that this could be approached. If you don't mind expanding your worksheet design to include two more cells, those cells could be used strictly for input and cells A1 and C1 could be used strictly for output. One of the input cells could contain the value to be converted and the other could contain the measurement unit of the input value (in or mm, for instance).

Of course, if you want to really limit yourself to two cells, then you will need to resort to using macros to do the actual conversion. You can use a worksheet event that is triggered every time a cell value is changed, and the event handler could check to see if the cell being changed is either A1 or C1. The following macro gives an example of how this could work:

Private Sub Worksheet_Change(ByVal Target As Range)
    Application.EnableEvents = False
    Select Case Target.Address
        Case "$A$1"
            [C1] = [A1] * 25.4
        Case "$C$1"
            [A1] = [C1] / 25.4
    End Select
    Application.EnableEvents = True
End Sub

Note that you don't have to have any formulas in cells A1 or C1; the formulas are in the macro itself. If there is a change in cell A1 (inches are entered by the user), then the value in cell C1 is changed by the macro. Likewise, if there is a change in cell C1 (millimeters are entered by the user), then the value in cell A1 is changed by the macro. A change in any other cell besides A1 or C1 is ignored by the macro.

Note:

If you would like to know how to use the macros described on this page (or on any other page on the ExcelTips sites), I've prepared a special page that includes helpful information. Click here to open that special page in a new browser tab.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (9581) applies to Microsoft Excel 2007, 2010, 2013, 2016, 2019, and Excel in Office 365. You can find a version of this tip for the older menu interface of Excel here: Developing Reciprocal Conversion Formulas.

Author Bio

Allen Wyatt

With more than 50 non-fiction books and numerous magazine articles to his credit, Allen Wyatt is an internationally recognized author. He is president of Sharon Parq Associates, a computer and publishing services company. ...

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What is 2 + 4?

2022-01-02 09:18:19

Mike

Please ignore my last comment. I have no idea why it did not work before, but I have just tried it again, in a new blank Worksheet, and the macro works just fine.


2022-01-01 13:52:13

Mike

The only way I could get the Macro to work as expected was to de-select 'After pressing Enter, move selection Direction' in Options. The cells were not updating until the input cell was selected again.

Adding some additional lines made it work for me.

Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False
Select Case Target.Address
Case "$A$1"
[C1] = [A1] * 25.4
Case "$C$1"
[A1] = [C1] / 25.4
Case "$B$1"
Range("A1").Select
Case "$D$1"
Range("C1").Select
Case "$A$2"
Range("A1").Select
Case "$C$2"
Range("C1").Select
End Select
Application.EnableEvents = True
End Sub


2022-01-01 06:02:09

Kiwerry

Not wanting to use macros, I use the following solution for conversions.
Example, temperatures: Unit1 in cell D3, unit 2 next to it in E3 (both with the appropriate custom formats for the units); the converted value is in F3, using this formula:

=IF(ISBLANK(E3)+ISBLANK(D3)=0,"Clear D3 or E3!",IF(ISBLANK(E3),(IF(ISBLANK(D3),"Enter °C in D3 or °F in E3.",TEXT(D3*9/5+32,"###0.0""°F"""))),TEXT(5/9*(E3-32),"###0.0""°C""")))

May not be the most elegant solution and uses an extra cell, but it does what I want it to.


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