Four outcomes and a small range
A d4 has four equally likely face values, so its average is (1 + 4) / 2 = 2.5. Each particular value has probability 25%. Its narrow range is the useful property: compared with a d20, a four-sided result changes a total by only a few points, which is why small random adjustments and low-damage effects often use this shape.
Reading a concrete damage roll
If a rule says 1d4 + 2 and the tool shows 3, the resolved amount is 5. The added 2 is fixed; only the face varies. Before rolling, the possible final amounts are 3, 4, 5, and 6, each with one-quarter probability. The expected final amount is 4.5, but that average should not replace the actual 3 shown in a single event.
A pyramid is not a percentage die
Physical d4s are commonly tetrahedral, but the geometry does not turn their faces into a continuum. The model assumes a value from 1 through 4, once each. It does not decide whether a game reads the upward face, a number at a vertex, or a special icon. Those conventions belong to the particular die or ruleset, not to the arithmetic of four labels.
Boundaries of this roll
This page does not add several d4s, apply advantage, or calculate whether a target is beaten after modifiers. A four-face draw is appropriate when the stated rule asks for exactly one small uniform integer. Once outcomes carry unequal effects, check the effect table rather than treating equal face odds as equal real-world consequences.
Comparing the four possible effects
A rule that assigns four different outcomes to the faces should inspect their consequences as well as their one-in-four odds. One outcome may cost a turn while another merely changes colour. Equal probability is a fact about selection; whether the outcomes are acceptable alternatives is a design decision made before the result.
Questions about this dice rule
What is the chance of the highest face?
One of four faces is highest, so the chance is 25%.
Can this page add a bonus?
Read the raw face here and apply a rule's fixed bonus separately.