diff --git a/cara/montecarlo.py b/cara/montecarlo.py
index e69de29b..34e59cc2 100644
--- a/cara/montecarlo.py
+++ b/cara/montecarlo.py
@@ -0,0 +1,11 @@
+import cara.models
+import numpy as np
+
+
+def calculate_qr(viral_load: float, emission_concentration: float, diameter: float, mask_efficiency: float,
+                 copies_per_quantum: float, breathing_rate: float = 1) -> float:
+    """
+    Calculates the quantum generation rate given a set of parameters.
+    """
+    volume = 4 * np.pi * (diameter / 2) ** 3 / 3
+    return viral_load * emission_concentration * volume * (1 - mask_efficiency) * breathing_rate / copies_per_quantum