This is a common question and there are essentially a number of answers, in order to work out which answer is correct for your situation we need to consider various factors such as…
What type of sign is it?
The type of sign will determine if there are any specific requirements you will need to follow in the design/creation of the sign. If the sign is a Health & Safety sign then there are guidelines you should follow with regards to the text size, font colour combination and even the position of the sign. For an in-depth look at Health & Safety Signage please read this article, Health & Safety Signage. If the sign is for a business, such as a sign above a shop window or on the outside of an office block you are probably not restricted in terms of font or colours. However, you may be limited by local planning laws, the local council or even your landlord if your premises are rented, be sure to check before you spend hard earned money on a sign that you are ultimately not able to erect.
How far away will people be when they see the sign?
This is probably the reason you are reading this article as this will ultimately determine the lettering size. We need to assume that we are talking about a person with 20:20 vision (or they are wearing glass/contacts to achieve 20:20 vision), we can then use the table below to work out the optimum lettering size based on the distance from the sign that we expect people to read it. Let’s take a sign that we want people be able to easily read from a distance of 25m, this could be a sign on building in an industrial estate and we want it readable as they come through the gate. You would need to make the letters 8” or 203mm tall for this to be easily read at the gate (25m away), however the sign would still be visible and potentially readable up to 106m away, ensuring that your business is also visible to passing traffic on the main road. If the sign is for a shop on the high street you may be looking at distances slightly less, maybe around 20m so you would look at a letter height of 6” or 150mm.
How big is the area available for the sign?
Another consideration factor is the area you have to mount the sign and what content you need to add to it. You now need to take into account the distance from which the sign will be read, what the important content is and ensure you do not make the sign bigger than the area you have. This can sometimes cause a trade off between the company name and the strap line, it is recommended that you ensure the company name is easily readable at the distance you need, this will bring the customers to your door, as they get closer they will be able to read the strap line.
Will it be illuminated or reflective?
Think about illumination of your sign, will you need it illuminated, probably in the winter months, but not so much in the summer. Think about how your sign could be viewed by the passing business, if it was illuminated would that turn peoples heads more than an unlit sign? If you have traffic that comes down the road towards you and their headlights shine towards your sign, you could be clever and add some reflective vinyl to your letters causing them to reflect back towards the traffic effectively popping off the front of the building and grabbing potential customers attention.