Rests

WHOLE

Thickness:

1/2 space.

Width: 

the width of the head of a quarter or half note.

Placement: 

When two voices are notated on the same staff: the upper rest is placed below the top staff line and the lower rest is placed beneath the lower staff line.

Beneath the 3rd staff line;

HALF

Thickness:

1/2 space.

Width: 

The width of the head of a quarter or half note. 

Placement: 

Top of the middle staff line, in vertical alignment with the beat to which it corresponds;
When two voices are notated on the same staff: upper rests sit on top staff line and lower rests sit on lower staff line. 

When to Use:

The half rest only takes the place of two quarter rests in cases where the measure in simple time can be divided into two equal halves. The half rest is never used in 3/4 meter.

QUARTER

Thickness:

1/2 space.

Width: 

The width of the head of a quarter or half note.