Please note:
This information is provided as a guideline and does not necessarily relate exactly in mathematical terms. Some scales are "cross overs" which could be used in either the smaller or larger scale.
Fraction Scale Millimeter Inch Height Train Gauge Actual Inch Scale
1/220 6.5 mm 1/4 Z Very Small Scale - less than 1/2 inch for most items
1/160 9 mm 3/8  N (OOO) .
1/144 14 mm ? N + - See Dragon Can.do Series for accurate representation.
1/120 15 mm 15/32 TT U.S. .
1/106 16 mm ? ? .
1/100 18 mm ? TT English Small Scale - usually 1 1/2 inches or less
1/90 . ? HO .
1/87 16.5-20 mm 5/8 HO Somewhat smaller than Matchbox.
1/76 19-20 mm 3/4 OO U.S. Matchbox Size
1/72 25 mm 1 OO Matchbox Size
1/64 26 mm 1 1/8 S Scale for all American Highway Legends
Straight chassis trucks = 4 inches long 
Semi Trailer trucks = 8 to 11 inches long. 
Lledo DG models fall into this range also.
1/56

1/50		 28 mm

35 mm		 1 3/16

1 1/4		 ?

O  -		 Scaled correctly for the 28mm Wargaming

Most tanks will measure 6 to 7 inches long. 
Lledo DG models fall into this range.
1/48 36 mm 1 1/2 O True 1:48 scale is 36mm
Most all Military Solido, Verem, Gasoline, Parade lines. 
Most tanks will measure 6 to 7 inches long. 
1/43 30-44 mm 1 3/4 O + Used often on 1/48 - 1/50 and  1/60 scale layouts
Some forced perspective may be required.
Most trucks will measure 4-5 inches long.
1/40 45 mm 1 7/8 ? .
1/35 50 mm 2 ? .
1/32 54 mm 2 1/4 ? Medium Scale for Vehicles = 6 to 10 inches
1/29 60 mm 2 1/2 G .
1/24 70-75 mm 3 G/#1 .
1/22 ? 3 1/3 G/#1 German .
1/20 ? 3 1/2 G/#1 U.S. .
1/18 90-100 mm 4 ? Large Scale - car or pickup = 9 to 12 inches
1/12 150 mm ? ? Common for 1940 - 60's Pressed Steel Buddy L
/Tonka Trucks
Trucks = 20 to 30 inches long 
1 inch = 1 foot in real life.
1/6 300 mm ? ? Very large Scale - uncommon for scaled vehicle use
but a few are out there - See 21st Century Toys.
More common for dolls and figures. 
2 inches = 1 foot in real life.