diff --git a/storm/Big.cpp b/storm/Big.cpp
index dcb2ab7..a8d7804 100644
--- a/storm/Big.cpp
+++ b/storm/Big.cpp
@@ -7,6 +7,23 @@ void SBigAdd(BigData* a, BigData* b, BigData* c) {
     Add(a->Primary(), b->Primary(), c->Primary());
 }
 
+void SBigBitLen(BigData* num, uint32_t* len) {
+    auto& buffer = num->Primary();
+    buffer.Trim();
+
+    auto index = buffer.Count() - 1;
+    auto high = buffer[index];
+
+    uint32_t bitIndex;
+    for (bitIndex = 31; bitIndex > 0; bitIndex--) {
+        if (((1 << bitIndex) & high)) {
+            break;
+        }
+    }
+
+    *len = (index * 32) + bitIndex + 1;
+}
+
 int32_t SBigCompare(BigData* a, BigData* b) {
     return Compare(a->Primary(), b->Primary());
 }
diff --git a/storm/Big.hpp b/storm/Big.hpp
index 8b6d7a1..291eea2 100644
--- a/storm/Big.hpp
+++ b/storm/Big.hpp
@@ -6,6 +6,8 @@
 
 void SBigAdd(BigData* a, BigData* b, BigData* c);
 
+void SBigBitLen(BigData* num, uint32_t* len);
+
 int32_t SBigCompare(BigData* a, BigData* b);
 
 void SBigDel(BigData* num);
diff --git a/test/Big.cpp b/test/Big.cpp
index 7acf347..f9f16b8 100644
--- a/test/Big.cpp
+++ b/test/Big.cpp
@@ -459,6 +459,74 @@ TEST_CASE("SBigAdd", "[big]") {
     }
 }
 
+TEST_CASE("SBigBitLen", "[big]") {
+    SECTION("returns bit length of 1") {
+        BigData* num;
+        SBigNew(&num);
+        SBigFromUnsigned(num, 1);
+
+        uint32_t len;
+        SBigBitLen(num, &len);
+
+        CHECK(len == 1);
+
+        SBigDel(num);
+    }
+
+    SECTION("returns bit length of 5") {
+        BigData* num;
+        SBigNew(&num);
+        SBigFromUnsigned(num, 5);
+
+        uint32_t len;
+        SBigBitLen(num, &len);
+
+        CHECK(len == 3);
+
+        SBigDel(num);
+    }
+
+    SECTION("returns bit length of 0xFFFF") {
+        BigData* num;
+        SBigNew(&num);
+        SBigFromUnsigned(num, 0xFFFF);
+
+        uint32_t len;
+        SBigBitLen(num, &len);
+
+        CHECK(len == 16);
+
+        SBigDel(num);
+    }
+
+    SECTION("returns bit length of 0xFFFFFFFF") {
+        BigData* num;
+        SBigNew(&num);
+        SBigFromUnsigned(num, 0xFFFFFFFF);
+
+        uint32_t len;
+        SBigBitLen(num, &len);
+
+        CHECK(len == 32);
+
+        SBigDel(num);
+    }
+
+    SECTION("returns bit length of 0x22222222AAAAAAAA") {
+        BigData* num;
+        SBigNew(&num);
+        uint64_t num_ = 0x22222222AAAAAAAA;
+        SBigFromBinary(num, reinterpret_cast<uint8_t*>(&num_), sizeof(num_));
+
+        uint32_t len;
+        SBigBitLen(num, &len);
+
+        CHECK(len == 62);
+
+        SBigDel(num);
+    }
+}
+
 TEST_CASE("SBigCompare", "[big]") {
     SECTION("compares 10 and 1") {
         BigData* a;