The maximum number of field mappings that can be created in HubSpot is 500. This total includes both contact and company field mappings.
Please note: adding field mappings between HubSpot and Salesforce can increase the number of API calls made to your Salesforce Organization. If a field mapping is unnecessary for keeping your data in sync, and up to date, you should removing the mapping. Unnecessary mappings will lead to extraneous API calls.