Looking at the shape of the bloodstain allows forensic scientist to determine which direction the blood was moving and the angle from which the blood fell.  As already discussed, a rounded blood droplet shows that the blood fell at a 90 degree angle but a more elongated blood droplet shows that the blood fell at an angle other than 90 degrees.

 
Blood fell at
 90 Degree

  
Blood fell at an angle other than 90 degrees

The tail or spine of the blood stain helps determine the direction the blood came from.  The tail points in the direction of travel.  See below for an example:
 

Blood came from this direction, hit the surface and continued to create the tail

To determine the angle the droplet fell, scientists use the angle of impact equation.

Impact angle = sin ⁻ˡ (width/length)

Things to Remember:

• Measure in cm or mm but keep the same units for length and width
• Always calculate what is in parenthesis first, so divide width/length and then find the arcsin (sin⁻ˡ)

Example:

W=2.6cm, L=5.9 cm  

Impact angle= sin ⁻ˡ(arcsin)  width/length

Angle of Impact (AOI)= sin⁻ˡ(2.6 cm/5.9 cm)
AOI=sin⁻ˡ(.44)
AOI= 26.2

The tail of the bloodstain is not included when calculating the angle of impact.
 

Check out Angle of Impact to see how the shape of the bloodstain changes as the angle of impact changes.  Click Angle of Impact Tab.