Modify or change the data type setting for a field

This article explains how to modify or change the data type applied to a table field in an Access database.

In this article

Understand data types

Change data types

Restrictions on changing data types

Understand data types

When you first design and build a database, you plan one or more tables, you plan the fields (columns) for each table, and you set a data type for each field. For example, if you need to store dates and times, you set a field to the Date/Time data type. If you need to store names and addresses, you set one or more fields to the Text data type, and so on.

Access provides many different data types, and each type has a specific purpose. For a full list of all supported data types across the various Access versions, see Data types for Access desktop databases and Introduction to data types and field properties.

For more information about creating and using lookup fields, see the article Add or change a lookup field that lets you store multiple values.

Finally, data types provide a basic form of data validation because they help ensure that users enter the proper types of data in your table fields. For example, you cannot enter text in a field set to accept only numbers.

Change data types

Before you follow these steps, remember that changing a data type might truncate (cut off) some or all of the data in a field, and in some cases may remove the data entirely. For information about how Access changes data when you change a data type, see the section Restrictions on changing data types, later in this article.

Note: In Access, you can set the data types for your table fields by working in either Datasheet view or Design view. Steps in this section explain how to set the data type in both views. When you set data types in Design view, you see an extra choice, Lookup Wizard. That choice is actually not a data type. Instead, you use the Lookup Wizard to create lookup fields, which link foreign key fields to other tables. By default, Access sets lookup fields to the Number data type.

Change data types in Datasheet view

  1. In the Navigation Pane, locate and double-click the table that you want to change.

    Access opens the table in Datasheet view.

  2. Select the field (the column) that you want to change.

  3. On the Fields tab, in the Properties group, click the arrow in the drop-down list next to Data Type, and then select a data type. Note, if you're using Access 2007 on the Datasheet tab, in the Data Type & Formatting group, click the arrow in the drop-down list next to Data Type, and then select a data type.

  4. Save your changes.

Change data types in Design view

  1. If you have the table open in Datasheet view, right-click the document tab for the table and click Design View.

    -or-

    If you do not have the table open, in the Navigation Pane, right-click the table that you want to change, and then click Design View on the shortcut menu.

  2. Locate the field that you want to change, and select a new data type from the list in the Data Type column.

  3. Save your changes.

Top of Page

Restrictions on changing data types

As a rule, you can change the data type of all fields, except for:

  • Number fields with the Replication ID property enabled.

  • OLE Object fields.

  • Attachment fields.

In addition, you can change most data types when a field contains data. However, depending on the original data type and the new data type that you want to use, Access might truncate or delete some data, or it may not allow the conversion at all.

The following table lists the possible data type conversions that you can perform in Access, and describes any restrictions that Access might impose on the conversion.

Convert to this type

From this type

Changes or restrictions

Text

Memo

Access deletes all but the first 255 characters.

Number

No restrictions.

Date/Time

No restrictions.

Currency

No restrictions.

AutoNumber

No restrictions.

Yes/No

The value -1 (Yes in a Yes/No field) converts to Yes. The value 0 (No in a Yes/No field) converts to No.

Hyperlink

Access truncates links longer than 255 characters.

Memo

Text

No restrictions.

Number

No restrictions.

Date/Time

No restrictions.

Currency

No restrictions.

AutoNumber

No restrictions.

Yes/No

The value -1 (Yes in a Yes/No field) converts to Yes. The value 0 (No in a Yes/No field) converts to No.

Hyperlink

No restrictions.

Number

Text

Text must consist of numbers and valid currency and decimal separators. The number of characters in the Text field must fall within the size set for the Number field.

For more information about the sizes of number fields, see the article Insert, create, or delete a field to store numeric values.

Memo

The Memo field must contain only text and valid currency and decimal separators. The number of characters in the Memo field must fall within the size set for the Number field.

For more information about the sizes of number fields, see the article Insert, create, or delete a field to store numeric values.

Number, but with a different field size or precision

Values must not be larger or smaller than what the new field size can store. Changing precision may cause Access to round some values.

Date/Time

The dates that you can convert depend on the size of the number field. Remember that Access stores all dates as serial dates and stores the date values as double-precision floating integers.

Access uses December 30, 1899 as date 0. Dates outside of the range April 18, 1899 and September 11, 1900 exceed the size of a Byte field. Dates outside the range April 13, 1810 and September 16, 1989 exceed the size of an Integer field.

To accommodate all possible dates, set the Field Size property of your Number field to Long Integer or larger.

For more information about serial dates and how Access uses and stores date values, see the article Enter a date or time value.

Currency

Values must not exceed (or fall below) the size limit set for the field. For example, you can convert a currency field to an Integer field only when those values are greater than 255 and do not exceed 32,767.

AutoNumber

Values must fall within the size limit set for the field.

Yes/No

"Yes" values convert to -1. "No" values convert to 0.

Hyperlink

Not applicable.

Date/Time

Text

Original text must be a recognizable date or date-time combination. For example, 18-Jan-2006.

Memo

Original text must be a recognizable date or date-time combination. For example, 18-Jan-2006.

Number

Value must fall between -657,434 and 2,958,465.99998843.

Currency

Value must fall between -$657,434 and $2,958,465.9999.

AutoNumber

Value must exceed -657,434 and be less than 2,958,466.

Yes/No

The value -1 (Yes) converts to December 29, 1899. The value 0 (No) converts to midnight (12:00:00 AM).

Hyperlink

Not applicable.

Currency

Text

Text must consist of numbers and valid separators.

Memo

Text must consist of numbers and valid separators.

Number

No restrictions

Date/Time

No restrictions, but Access may round the value

AutoNumber

No restrictions

Yes/No

The value -1 (Yes) converts to $1. The value 0 (No) converts to 0$.

Hyperlink

Not applicable.

AutoNumber

Text

Not allowed if the AutoNumber field serves as a primary key.

Memo

Not allowed if the AutoNumber field serves as primary key.

Number

Not allowed if the AutoNumber field serves as a primary key.

Date/Time

Not allowed if the AutoNumber field serves as a primary key.

Currency

Not allowed if the AutoNumber field serves as a primary key.

Yes/No

Not allowed if the AutoNumber field serves as a primary key.

Hyperlink

Not applicable.

Yes/No

Text

Original text must consist only of Yes, No, True, False, On, or Off.

Memo

Original text must consist only of Yes, No, True, False, On, or Off.

Number

Zero or Null converts to No, all other values convert to Yes.

Date/Time

Null or 12:00:00 AM converts to No, all other values convert to Yes.

Currency

Zeroes and Nulls convert to No, all other values to Yes.

AutoNumber

Access coverts all values to Yes.

Hyperlink

Not applicable.

Hyperlink

Text

If the original text contains a valid Web address, such as adatum.com , www.adatum.com, or http://www.adatum.com, Access converts the text to a hyperlink. Access tries to convert other values, meaning that you see underlined text, and the mouse cursor changes when you point at the link, but the links do not work. The text can contain any valid Web protocol: http://, gopher://, telnet://, ftp://, wais://, and so on.

Memo

See the previous entry. The same restrictions apply.

Number

Not allowed when a Number field is part of a relationship. If the original value is in the form of a valid I.P. address (four number triplets separated by a period: nnn.nnn.nnn.nnn) and the numbers happen to coincide with a Web address, the conversion results in a valid link. Otherwise, Access appends http:// to the beginning of each value, and the resulting links are not valid.

Date/Time

Access appends http:// to the beginning of each address, but the resulting links will almost never work.

Currency

Access appends http:// to the beginning of each value, but like dates, the resulting links will almost never work.

AutoNumber

Not allowed when the AutoNumber field is part of a relationship. Access appends http:// to the beginning of each value, but the resulting links will almost never work.

Yes/No

Access converts all Yes values to -1 and all No values to 0, and appends http:// to the beginning of each value. The resulting links do not work.

Top of Page

Connect with an expert
Contact us
Expand your skills
Explore training

Was this information helpful?

Thank you for your feedback!

Thank you for your feedback! It sounds like it might be helpful to connect you to one of our Office support agents.

×