From BlenderWiki

Scale

Description

Pressing S will enter the “scale” transformation mode where the selected object or data is scaled inward or outward according to the mouse pointer’s location. The object/data’s scale will increase as the mouse pointer is moved away from the pivot point, and decrease as the pointer is moved towards it. If the mouse pointer crosses from the original side of the pivot point to the opposite side, the scale will continue in the negative direction, making the object/data appear flipped (mirrored). The precision of the scaling is determined by the distance from the mouse pointer to the object/data when the scaling begins.

Options

LMB or ↵ Enter

Confirm the scale, and leave the object or data at its current scale on the screen.

MMB or selecting Scale on Axis option

Constrain the scaling to the X, Y or Z axis. This will modify the proportions of the object or data, making it longer, broader… See Axis Locking.

RMB or Esc

Cancel the scale, and return the object or data to its original scale.

Wheel

Object mode

Zoom in/out

Edit mode

• Proportional Editing disabled: Wheel does zoom in/out
• Proportional editing enabled: only vertices within the circle of influence are moved. In this case scroll the Wheel to change the radius of the the circle of influence.

AltS (Edit mode only)

Scales along the selected normal direction.

Center point of scale

To select the center point of scale (so-called “pivot point”!) use the “rotation/scaling” button accessed in the header of the 3D window, . For a full description of the different pivot points, see their dedicated page.