diff --git a/Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp b/Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp
index 0abf836ec24..0294976ed45 100644
--- a/Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp
+++ b/Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp
@@ -147,6 +147,20 @@ ErrorOr<String> UnsignedBigInteger::to_base(u16 N) const
     return StringView(buffer.bytes().slice(0, written - 1)).to_ascii_lowercase_string();
 }
 
+size_t UnsignedBigInteger::count_digits_in_base(u16 base) const
+{
+    VERIFY(base <= 36);
+
+    if (is_zero())
+        return 1;
+
+    int size = 0;
+    MP_MUST(mp_radix_size(&m_mp, base, &size));
+
+    // mp_radix_size includes a null byte.
+    return static_cast<size_t>(size) - 1;
+}
+
 u64 UnsignedBigInteger::to_u64() const
 {
     return mp_get_u64(&m_mp);
diff --git a/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h b/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h
index bb7ac6862f4..53900083b1f 100644
--- a/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h
+++ b/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h
@@ -47,6 +47,8 @@ public:
     [[nodiscard]] static ErrorOr<UnsignedBigInteger> from_base(u16 N, StringView str);
     [[nodiscard]] ErrorOr<String> to_base(u16 N) const;
 
+    [[nodiscard]] size_t count_digits_in_base(u16 base) const;
+
     [[nodiscard]] u64 to_u64() const;
 
     enum class RoundingMode {
diff --git a/Tests/LibCrypto/TestBigInteger.cpp b/Tests/LibCrypto/TestBigInteger.cpp
index 61c5abd4e0e..8ff95c56cfe 100644
--- a/Tests/LibCrypto/TestBigInteger.cpp
+++ b/Tests/LibCrypto/TestBigInteger.cpp
@@ -209,6 +209,31 @@ TEST_CASE(test_unsigned_bigint_base10_to_string)
     EXPECT_EQ(result, "57195071295721390579057195715793");
 }
 
+TEST_CASE(test_unsigned_bigint_count_digits)
+{
+    constexpr auto count_digits = [](u64 number, u16 base) {
+        u8 digits = 0;
+
+        do {
+            number /= base;
+            ++digits;
+        } while (number > 0);
+
+        return digits;
+    };
+
+    for (auto base : to_array<u16>({ 2, 8, 10, 16 })) {
+        for (auto test : to_array<u64>({ 0, 9, 10, 19, 99, 100, 999, 1000, 9999, 10000, 99999, 10000000000, 99999999999 })) {
+            auto bigint = Crypto::UnsignedBigInteger { test };
+
+            auto result = bigint.count_digits_in_base(base);
+            auto expected = count_digits(test, base);
+
+            EXPECT_EQ(result, expected);
+        }
+    }
+}
+
 static size_t count_leading_zeros(Bytes data)
 {
     auto leading_zeros = 0u;