diff --git a/monitor/tach_sensor.cpp b/monitor/tach_sensor.cpp
index 2bf7b06..33904bd 100644
--- a/monitor/tach_sensor.cpp
+++ b/monitor/tach_sensor.cpp
@@ -74,7 +74,7 @@
                        bool hasTarget,
                        size_t funcDelay,
                        const std::string& interface,
-                       size_t factor,
+                       double factor,
                        int64_t offset,
                        size_t timeout,
                        const sdeventplus::Event& event) :
diff --git a/monitor/tach_sensor.hpp b/monitor/tach_sensor.hpp
index 27a036e..b2b9c50 100644
--- a/monitor/tach_sensor.hpp
+++ b/monitor/tach_sensor.hpp
@@ -88,7 +88,7 @@
                    bool hasTarget,
                    size_t funcDelay,
                    const std::string& interface,
-                   size_t factor,
+                   double factor,
                    int64_t offset,
                    size_t timeout,
                    const sdeventplus::Event& event);
@@ -125,7 +125,7 @@
         /**
          * @brief Returns the factor of the sensor target
          */
-        inline size_t getFactor() const
+        inline double getFactor() const
         {
             return _factor;
         }
@@ -272,7 +272,7 @@
         /**
          * @brief The factor of target to get fan rpm
          */
-        const size_t _factor;
+        const double _factor;
 
         /**
          * @brief The offset of target to get fan rpm
diff --git a/monitor/types.hpp b/monitor/types.hpp
index 6604778..3048961 100644
--- a/monitor/types.hpp
+++ b/monitor/types.hpp
@@ -43,7 +43,7 @@
 using SensorDefinition = std::tuple<std::string,
                                     bool,
                                     std::string,
-                                    size_t,
+                                    double,
                                     int64_t>;
 
 constexpr auto fanNameField = 0;