Most transfer services impose minimum and maximum transfer amounts, but the exact amounts vary. Check with your service provider to find out what limits apply to your transfer. Note that some services may raise your maximum transfer amount if you provide additional documents to verify your identity and employment.
Legally, there are no limits to the amount you can send out of the US. But you may be required by law to provide extra personal and/or employment information for large transfers. These laws are designed to track and prevent illegal financial activities such as fraud and terrorist financing.