Bloodstain Pattern
Analysis Calculator
Calculate impact angles and origin height using standard trigonometric formulas used in forensic reconstruction.
🧬 BPA ANALYZER v2.0
Bloodstain Pattern Analysis & Trajectory Reconstruction
Evidence Log
1. Measure
Measure width and length of the stain. Exclude the tail (spines) of the drop; measure only the main elliptical body.
2. Calculate Angle
Use the calculator to determine the angle of impact (θ) using the formula sin(θ) = Width / Length.
3. Find Origin
Input the distance to the wall or source to approximate the height (Z-axis) of the origin point using tan(θ).
# The Physics of Bloodstains
When a spherical drop of blood strikes a surface at an angle, it elongates into an ellipse. The relationship between the width and length of this ellipse allows forensic experts to calculate the angle at which the drop struck the surface (Angle of Impact).
θ = arcsin( Width / Length )Height = tan( θ ) × DistanceWhy width is always ≤ length: A drop striking at 90° (perpendicular) creates a perfect circle (Width = Length). As the angle decreases (becomes more acute), the stain elongates, increasing length while width remains relatively constant to the drop's volume. Thus, the ratio W/L is always between 0 and 1, matching the domain of the sine function.
Correct Measurement Technique
Precision is critical in BPA. The most common error in manual calculation is including the "tail" or "scallops" of the stain in the length measurement.
- ❌ WRONG:Measuring the entire stain including thin spines or satellite spatter.
- ✅ RIGHT:Fit a best-fit ellipse over the main body of the stain. Measure the major (Length) and minor (Width) axes of this ellipse.
Frequently Asked Questions
Can this calculator be used for real crime scenes?
No. This is an educational tool. Real forensic analysis involves complex variables such as surface tension, viscosity, air resistance, and surface texture (roughness) which significantly alter stain formation. Court-admissible analysis requires certified experts using validated software.
What is the "Area of Convergence"?
The Area of Convergence is the 2D point on a surface (usually the floor or a wall) where the reverse trajectories of multiple stains intersect. By combining this with the impact angle (3D), analysts can find the "Area of Origin" in 3D space.
What does an angle of 10° look like?
A very acute angle like 10° produces a long, thin streak. An angle of 90° produces a perfect circle. An angle of ~45° produces an oval where the length is roughly 1.4 times the width.
DISCLAIMER: The results provided by this calculator are for theoretical and educational purposes only. They do not account for physical drag, gravity (beyond basic trigonometry), or surface interaction properties. Do not use for legal, medical, or safety-critical applications.