Irvine is about 1.3 times smaller than Seattle.

Seattle is approximately 217 sq km, while Irvine (map shows its 24 named neighbourhoods; the area covers the whole city) is approximately 170 sq km, making Irvine 78.2% the size of Seattle.
Tip: This to-scale comparison of Seattle vs. Irvine uses the Mercator projection, which distorts the size of regions near the poles.
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