If the metric system gives you heartburn, here are a few tips to help you out.

The Truth (to within 3 or 4 significant digits)		What you can remember (You'll be about 10% too short.)
1 meter	= 3.280 feet = 1.094 yards	1 meter	~= 3 feet ~= 1 yard
100 m	= 109 yards	100 m	~= 100 yards ~= length of a football field
1000 m	= 1 kilometer = 1 km = 0.621 miles ~= 5/8 mile	1000 m	~= 1/2 mile