If you wear a size 28, in AUS, you'd generally be a size 10.
For example, a size 10, a medium, and a waist size 28 are all the same size…
Australian sizes are measured the same as the UK. So if you're a 10 in Australia, you'll need a 10 from a UK-based store. If you're purchasing from an American store, you'll need to go 2 sizes smaller. So if you're a 10 in Australia, you're a 6 in the US.
As an average, a Medium is likely to be a around a size 12. Generally a Small will be an AU 8-10 and a Large an AU 14-16. An Extra Small is likely to be a size 6, with an Extra Large likely to be a size 18.
Jeans sizes in the US are based on the waist/length ratio, given in inches (in). For example, a male with the jeans waist size of 28 in and leg length of 30 in will have a jeans size of 28/30. We can also use the standard S/M/L sizes, or the simple numerical value (30-50 for men, 0-30 for women).
Waist Size: XS or extra small means 28–30 inches (71–76 cm), S or Small means 30–32 inches (76–81 cm), M or Medium means 32–34 inches (81–86 cm), and L or Large means 34–36 inches (86–91 cm).
If you wear a size 28, in AUS, you'd generally be a size 10.
Italian and other European sizes are typically converted from American, British and Australian sizes, by adding 10. For example, a 38 suit in Australia would be an Italian 48.
While some jeans come in regular UK sizes, such as 6 or 16, many offer more precise sizing. For example, a size 10 is a jeans size 28. However, if you find you're in-between sizes, a waist 29 pair of jeans equates to a size 11.