1 gauge

Gauge 1
Gauge 1 model of a Ruston & Hornsby locomotive
Scale	3⁄8 inch to 1 foot ca. 10 mm to 1 ft
Scale ratio	ca. 1:32
Model gauge	1.75 in (44.45 mm)
Prototype gauge	4 ft 8 1⁄2 in (1,435 mm) standard gauge

1 gauge, gauge 1 or gauge one is a model railroading and toy train standard that was popular in the early 20th century, particularly with European manufacturers. Its track measures 1.75 in (44.45 mm), making it larger than 0 gauge but slightly smaller than wide gauge, which came to be the dominant U.S. standard during the 1920s.

Gauge one was standardised, according to Model Railways and Locomotive magazine of August 1909, at 1.75 in (44.45 mm). An exact 1:32 scale would yield 1.766 in (44.85 mm) for standard gauge prototype. The distance between the wheel tyres was set at 1 ¹⁷⁄₃₂ in (38.894 mm) and between the centre of the track 48 mm (no inch equivalent suggesting it was metric users' requirement only). The wheel width was set at ¹⁹⁄₆₄ in (7.541 mm).

Definitions using gauge, rather than scale, were more common in the early days with the four gauges for which standards were adopted being No. 0 (commonly called O gauge currently), No. 1, No. 2 and No. 3.

Initially as popular in the United States as in the UK, 1 gauge lost popularity in the U.S. due to World War I, which dramatically decreased foreign imports, allowing the U.S. wide gauge standard to gain traction. After World War I, most surviving U.S. manufacturers switched to wide gauge. In the UK and the rest of the world, 1 gauge also declined, although more slowly, and by the 1940s had practically disappeared.

In the 1950s and 1960s 1 gauge experienced a renaissance, first in the UK and then elsewhere. This was helped by 1 gauge being the same size as the modern G scale, a popular standard for outdoor model railroads.

Although vintage 1 gauge trains use the same track standard as modern G scale, scale modeling was not a primary design consideration in 1 gauge's heyday, so the actual size and scale of the locomotives and cars varied. Generally, 1 gauge equipment works out to approximately 1:32 scale (roughly 10mm = 1 foot). G scale at 1:22.5 means the 1 gauge track represents 1,000 mm (3 ft 3 ³⁄₈ in) metre gauge track. Such railways are to be found in, among other places, Switzerland, the inspiration source for many commercial G gauge models.