https://support.coinbase.com/customer/en/portal/articles/815435-does-coinbase-pay-miner-fees-?b_id=13521
The fee you pay for outgoing transactions is calculated dynamically at the time the transaction is created. This means that the fee may be higher or lower depending on the overall transaction volume currently on the digital currency network. The fees are displayed on the send confirmation screen. Please note that no portion of this fee goes to Coinbase.
Would be great to hear from someone whom has sent Bitcoin from Coinbase to another wallet and what it cost in miner fees percent wise please.