The standard gauge in Europe is 1,435 millimeters (which is 4 feet 8.5 inches). This measurement is used by the vast majority of railway networks across the continent, including Great Britain, France, Germany, Italy, and the Benelux countries. It is often referred to as the "Stephenson gauge" after the British railway pioneer George Stephenson. The use of a uniform gauge allows for the seamless operation of international high-speed trains like the Eurostar, Thalys, and TGV across national borders. However, there are notable exceptions to this standard. Spain and Portugal traditionally use "Iberian gauge" (1,668 mm), and Finland and the Baltic states (Estonia, Latvia, Lithuania) use "Russian gauge" (1,520 mm), which dates back to the era of the Russian Empire. Despite these differences, most new high-speed lines built in Spain and the Baltics (such as the Rail Baltica project in 2026) are being constructed using the 1,435 mm standard gauge to better integrate with the rest of the European Union's rail infrastructure. This standardization is critical for the "Single European Railway Area," aimed at making rail travel as efficient and interconnected as air travel across the entire continent.