Western Australia (WA) spans ~2,529,875 km². The United Kingdom covers ~243,610 km².
Calculation: 2,529,875 ÷ 243,610 ≈ 10.38
So you could fit the UK into Western Australia a little over 10 times—with room to spare.
Next time you look at a map, imagine ten United Kingdoms laid out across the western third of Australia. That's Western Australia.