diff --git a/src/BUILD b/src/BUILD
index a8965f0..b268e1c 100644
--- a/src/BUILD
+++ b/src/BUILD
@@ -8,6 +8,16 @@ cc_library(
   ],
 )
 
+cc_library(
+  name = "montecarloLib",
+  srcs = [
+    "montecarlo.cpp"
+  ],
+  hdrs = [
+    "montecarlo.h"
+  ],
+)
+
 cc_binary(
   name = "mainProg",
   srcs = [
@@ -16,5 +26,6 @@ cc_binary(
   ],
   deps = [
     ":factorLib",
+    ":montecarloLib",
   ], 
 )
\ No newline at end of file
diff --git a/src/main.cpp b/src/main.cpp
index f084620..22870bd 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -25,4 +25,8 @@ int main(int argc, char** argv)
     cout << result << ",";
   }
   cout << endl;
+
+  auto monteCarloPi = MonteCarloPi();
+  double pi = monteCarloPi.estimatePi();
+  cout << "The estimated pi is: " << pi << endl;
 }
\ No newline at end of file
diff --git a/src/main.h b/src/main.h
index 8f38a45..1342c80 100644
--- a/src/main.h
+++ b/src/main.h
@@ -4,5 +4,6 @@
 #include <iostream>
 #include <stdexcept>
 #include "factor.h"
+#include "montecarlo.h"
 
 #endif
\ No newline at end of file
diff --git a/src/montecarlo.cpp b/src/montecarlo.cpp
index e69de29..6b796dd 100644
--- a/src/montecarlo.cpp
+++ b/src/montecarlo.cpp
@@ -0,0 +1,42 @@
+#include "montecarlo.h"
+
+using namespace std;
+
+const int NUM = 8;
+const int NUM_EACH_THREAD = 10000000;
+
+MonteCarloPi::MonteCarloPi()
+{
+  inCircleVec.resize(NUM, 0);
+}
+
+void MonteCarloPi::estimatePiSingleThread(int threadId)
+{
+  random_device rd;
+  // mersenne_twister_engine seeded with rd()
+  mt19937 gen(rd());
+  uniform_real_distribution<double> distrib(0.0, 1.0);
+  for(int i = 0; i < NUM_EACH_THREAD; i++)
+  {
+    double x = distrib(gen);
+    double y = distrib(gen);
+    if (x*x + y*y <= 1.0)
+      inCircleVec[threadId]++;
+  }
+}
+
+double MonteCarloPi::estimatePi()
+{
+  for(int i = 0; i < NUM; i++)
+  {
+    threads.emplace_back(&MonteCarloPi::estimatePiSingleThread, this, i);
+  }
+
+  for(auto& t : threads)
+  {
+    t.join();
+  }
+
+  // return pi here
+  return (4.0 * accumulate(inCircleVec.begin(), inCircleVec.end(), 0) / (NUM * NUM_EACH_THREAD));
+}
\ No newline at end of file
diff --git a/src/montecarlo.h b/src/montecarlo.h
index e69de29..9e7743e 100644
--- a/src/montecarlo.h
+++ b/src/montecarlo.h
@@ -0,0 +1,28 @@
+#ifndef MONTE_H
+#define MONTE_H
+
+#include <iostream>
+#include <vector>
+#include <random>
+#include <thread>
+#include <algorithm>
+
+using namespace std;
+
+class MonteCarloPi
+{
+public:
+  MonteCarloPi& operator=(const MonteCarloPi&) = delete;
+
+  MonteCarloPi();
+  ~MonteCarloPi() = default;
+
+  void estimatePiSingleThread(int threadId);
+  double estimatePi();
+
+private:
+  vector<thread> threads = {};
+  vector<int> inCircleVec = {};
+};
+
+#endif
\ No newline at end of file