I wish I could remember the exact quote, but in the diary of a German soldier fighting on in France he said something like "For every Krupp shell we sent to the Americans, they sent a hundred Detroit shells back."
In "The Rommel Papers," (which is incidentally a really splendid book that you should definitely read if you have any interest in tactics at all), Rommel himself claims that the ratio was in practice closer to 500:1 in the African theater.
If Wikipedia is to be believed, the US produced more M4 chassis (all vehicle types) in 1943-alone (21,231, admittedly a huge surge in yoy production) [1] than Germany produced of any single chassis type during the whole war (most numerous: Pz III at 15,747 total) [2].
