What is the effect of one point of block skill?

I have been unable to find the exact value of one point of blocking. The unofficial Elder Scrolls pages and other wikis do not list a value for blocking.

As an example, for heavy armor one point adds 0.4% armor.

The block value seems important because I want to find out how much fortify block to enchant on my stuff. the USEP lists the max block mitigation as 85% (if you are looking at this page) or 80% (if you are looking at this page).

Solution 1:

The numbers on UESP are likely guesstimates added before the Creation Kit was released.

According to actual game values and assuming no other combat modifications, the base block value (fBlockSkillBase) is 0% mitigation at 0 skill, and each point of skill increases that mitigation by 2% (fBlockSkillMult) up to a maximum of 70% (fBlockMax).

However, there are several dozen other factors—ranging from whether you're staggered to whether you're using a weapon to block—that affect your block mitigation percentage. You can find these multipliers in the Creation Kit by going to Gameplay → Settings... and searching for "block".

Solution 2:

Not an exact number, but the answer to your larger question seems to be: With a Daedric shield, you need a total of +32.5% increased block effectiveness to reach the block mitigation cap of 85% at a block skill of 100.

So, you could achieve that with 4 ranks in the shield wall perk, and a non-enchanted shield. Different shields seem to have different block ratings. A glass shield needs more like 37.5%. A hide shield would seem to need around 46%.

Information taken from this thread.