Angle of Impact Calculator
Calculate the angle of impact of blood spatter from ellipse width and length measurements for forensic crime scene reconstruction. Use our free Angle of Impact
What Is the Angle of Impact?
In forensic bloodstain pattern analysis, the angle of impact is the angle between the surface and the trajectory of a blood droplet. It ranges from near 0 degrees (low, elongated stains) to 90 degrees (circular drops from a vertical drip).
Angle of Impact Formula
$$\alpha = \arcsin\left(\frac{W}{L}\right)$$Measure the minor axis ($W$, width) and major axis ($L$, length) of the elliptical stain. Ignore any tail on the spatter when measuring.
Estimating Origin Height
When you know the horizontal distance from the stain to the blood source, you can estimate height using:
$$h = d \times \tan(\alpha)$$Related tools: Right Triangle Calculator and Arcsin Calculator.
Frequently Asked Questions
What measurements do I need?
Measure the width (minor axis) and length (major axis) of the blood spatter ellipse in centimeters. Width must not exceed length.
Why is width divided by length?
A droplet hitting at 90 degrees forms a circle where width equals length. Lower angles stretch the stain, reducing the width-to-length ratio.
How accurate is this method?
Real crime scenes involve gravity, surface texture, and droplet velocity. This formula is a simplified approximation and can have significant error margins.
What is stringing in forensics?
Stringing connects multiple stains using their angles and directions to locate an area of convergence where blood likely originated.
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