What is the assumed tolerance of a carbon resistor if there is no fourth color band present?

When a carbon resistor does not have a fourth color band, it is typically assumed to have a tolerance of 20%. Resistors are often marked with a color coding system to indicate their resistance value and tolerance. The first two or three bands represent the resistance value, while the fourth band indicates the tolerance level – a measure of how much the actual resistance can vary from the stated value.

In the absence of a fourth band, standard practice defines the tolerance at 20%. This convention is especially relevant for carbon resistors, which are often less precise than other types, such as metal film resistors that typically come with better tolerances like 5% or 1%. Thus, when recognizing resistors without the fourth band, it's critical to remember the general assumption that they will likely have a tolerance of 20%.