Your choice of the size of warning sign will depend on factors such as the location of the sign, viewing conditions (low light vs. adequate lighting, distractions around the sign, etc.), the amount of text and/or the number of symbols on the sign, and the safe viewing distance. Warning safety signs usually have these standard sizes - 7”x5”, 10”x7”, 14”x10”, and 20”x14” with a safe viewing distance of 8ft., 10ft., 20ft., and 30ft. respectively.  ANSI also provides guidance about the letter size on the warning safety sign as per the minimum safe viewing distance, where the letter height measurement is based on the height of the capital letter ‘H’ in the message. The height of the signal word is required to be at least 50% greater than the letter height of the majority of the sign legend. You may refer to the table below to understand the letter sizing requirements. Minimum safe viewing distance (feet) Minimum letter height of letter 'H' in the sign legend (points) Minimum letter height of the signal word (inches) 8 32 0.48 10 40 0.60 20 80 1.20 30 120 1.80