Can someone explain

Can someone explain bitterness ratio in simple terms?
In doing a recipe, an ESB, Beersmith shows a bitterness ratio of .772%.

I found my answer but I don't know how to delete this ?.

IBUs divided by Original Gravity points

so if your IBUs were 35 and your original gravity was 1.048, your bitterness ratio would be 35/48 = 0.729

It gives you some idea of the balance of the beer. More malty and higher ABV beers (higher OG) generally need more IBUs to balance it out. Different styles of beer tend to have a range of bitterness ratios that are "standard" for the style - more malty styles (e.g. Irish Reds) have a low bitterness ratio whereas more bitter styles (e.g. IPAs) have a high bitterness ratio . I remember seeing a list somewhere that gives target bitterness ratios for different brews. I'll see if I can track it down.

[EDIT: see next response]

I couldn't find what I was looking for so I went ahead and ran the numbers myself. Here is a range of bitterness ratios by style that I created using the 2008 BJCP Style Guidelines.

Bitterness Ratio Guide

Remember that these values are just guidelines if you are looking to brew to style, not hard-and-fast rules of brewing (are there any of those?).