Knots (kts) = nautical miles per hour (nmph).
1 nautical mile = 6,000 feet.
1 statute (land) mile = 5,280 feet.
MPH = statute miles per hour
1 mile = .88 nmile
None of this has anything to do with the metric system.
KPH = kilometers per hour
1 kilometer ≈ 3,281 feet ≈ .62 mile ≈ .547 nmile