Rail gauge is the distance between the inner sides of the heads of the two parallel rails that make up a single railway line. Sixty percent of the world's railways use a standard gauge of 1,435 mm (4 ft 8+1⁄2 in). Wider gauges are called broad gauge; smaller gauges, narrow gauge. Break-of-gauge refers to the meeting of different gauges. Some stretches of track are dual gauge, with three or four rails, allowing trains of different gauges to share them.

*****************
Gauge ↓ Name ↓ Installation ↓ Usage ↓
1,676 mm (5 ft 6 in) Indian gauge >77,000 km India (42,000 km; increasing with Project Unigauge), Pakistan, Argentina (24,000 km), Chile
(approx. 61⁄2% of the world's railways)
1,668 mm (5 ft 5+2⁄3 in) Iberian gauge 14,300 km Portugal, Spain
1,600 mm (5 ft 3 in) Irish gauge 9,800 km Ireland and important minor gauge in Australia - Victorian gauge (4,017 km), Brazil (4,057 km)
1,524 mm (5 ft) Russian gauge 7,000 km ...more

1'6"-2'6" (500-750mm): Small Narrow Gauge
2'6"-3'6" (750mm-1000mm): Large Narrow Gauge
3'6"-4'8" (1000-1435mm): Narrow Full Size
4'8" (1435mm): Standard Gauge
4'8"-5'6" (1435-1700mm): Broad Full Size
Greater than 5'6" (1700mm): Broad Gauge

Broad gauge with width of 5' 6" , meter gauge (tracks a meter apart) and the narrow gauge (2' 6")

Narrow Gauge : 762 mm
meter gauge : 1 meter
Broad guage : 1676 mm

Meter gauge = 1000 mm
broad gauge is probably 1670 mm

Narrow Gauge is approx. 2 feet. 2. Metre gauge is 3' 3/8" and Broad gauge is 5'.6"