The meridian 78° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Atlantic Ocean, the Caribbean Sea, Panama, South America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole. The 78th meridian west forms a great circle with the 102nd meridian east.

From Pole to Pole

Starting at the North Pole and heading south to the South Pole, the 78th meridian west passes through: ! scope="col" width="120" | Co-ordinates ! scope="col" | Country, territory or sea ! scope="col" | Notes ! scope="row" style="background:#b0e0e6;" | Arctic Ocean ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Baffin Bay ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Baffin Bay ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Eclipse Sound ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Foxe Basin ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Foxe Basin ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Foxe Channel ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Foxe Channel ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Foxe Channel ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Hudson Bay ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Hudson Bay ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Hudson Bay ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Hudson Bay ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Lake Ontario ! scope="row" | 🇺🇸 ! scope="row" style="background:#b0e0e6;" | Atlantic Ocean ! scope="row" | 🇧🇸 ! scope="row" style="background:#b0e0e6;" | Atlantic Ocean ! scope="row" | 🇧🇸 ! scope="row" style="background:#b0e0e6;" | Atlantic Ocean ! scope="row" | 🇨🇺 ! scope="row" style="background:#b0e0e6;" | Caribbean Sea ! scope="row" | 🇯🇲 ! scope="row" style="background:#b0e0e6;" | Caribbean Sea ! scope="row" | 🇵🇦 ! scope="row" style="background:#b0e0e6;" | Pacific Ocean ! scope="row" | 🇨🇴 ! scope="row" | 🇪🇨 ! scope="row" | 🇵🇪 ! scope="row" style="background:#b0e0e6;" | Pacific Ocean ! scope="row" style="background:#b0e0e6;" | Southern Ocean ! scope="row" | Antarctica