The number of custom fields you can have depends on which plan you are on. You can learn more about usage limits in this article
Custom fields can be used when the information you want to add to Pipedrive doesn't exist as a default field. For example, there is no default field for 'Job Title' for people contacts. If you wanted to include that information, however, you could select a single option or text type custom field under people contacts, and call it 'Job Title' to be able to easily include that information for your Pipedrive contacts.
There are sixteen different types of custom fields. The type of custom field you choose will depend on what kind of information you want to add to your deals, contacts, or products.
Text - Notes or other text. These fields store up to 255 characters
Useful for: Billing addresses, secondary email addresses, (short) comments, job titles
Autocomplete - Note that auto-fills based on previous inputs, stores up to 255 characters
Useful for: Custom options (e.g. tagging), email addresses.
Large text - Longer notes
Useful for: Comments, descriptions
Numerical - Numerical data
Useful for: Commission, priority level
Monetary - Numerical data prefixed with a currency symbol. The currency of the Monetary custom field will match your default currency setting unless otherwise specified.
Useful for: Commission, amounts
Multiple options - List of predefined options where multiple can be selected (Maximum 500 options).
Useful for: Industry, region, competitors, job title, tags
Single option - List of predefined options where only one can be selected (Maximum 500 options).
Useful for: Lead type, category, industry, job title
Time - Specific time that is chosen using time drop-down. Time format will match your default time zone format.
Useful for: Delivery time, lunchtime
Time range - Time range that is chosen using time drop-down. Time format will match your default time zone format.
Useful for: Office hours, best time in the day to contact
Date - Specific date that is chosen from a drop-down calendar
Useful for: Delivery date, deadlines
Date range - Date range that is chosen from a drop-down calendar
Useful for: Event dates, completion estimates, holidays
The following five custom field types can be used as secondary fields for fields that already exist. They will behave like the corresponding default fields in Pipedrive, and often will refer to actual items in Pipedrive.
For example, if a deal has two related organizations, you could link the primary organization to the deal with the default linking feature, and then create an organization type custom field called 'Secondary Organization' under deals to be able to list the second organization. This is commonly used as a workaround since a deal can only be linked to one organization at a time by default.
User* - Tag a Pipedrive user from your Pipedrive account
Useful for: Previous or secondary deal or contact owners, other users related to that deal or contact.
Organization* - Allows for tagging an additional organization from your Pipedrive organizations. If the organization added under the organization type custom field does not exist in the Pipedrive database yet, it will be created as a new organization.
Useful for: Related or secondary parties, partner organizations
Person* - Allows for tagging an additional person from your Pipedrive database. If the person contact added under the person type custom field does not exist in the Pipedrive database yet, it will be created as a new person contact.
Useful for: Related or secondary person contact
Address - Full addresses stored using autocomplete from Google Maps. Organizations in Pipedrive already have a default address, but an address type custom field can be added when adding a secondary address to organizations, or when you want to add an address directly to a deal or contact person.
An address type custom field will behave just like the default address field under organizations, including subfields and the 'show on map' ability.
Useful for: Event places, secondary office locations (when separate from business address)
Phone - Allows for a phone number of a Skype user name to be entered with click to call functionality. People contacts in Pipedrive already have a default phone field, but a phone type custom field can be added under organizations or deals if you want a phone number to be listed under another item.
Useful for: Secondary Skype names, secondary phone numbers, org/deal specific contact information
*User, Organization, and Person type custom fields will allow you to click through directly to the item that is entered in those values.