diff --git a/libluna/include/luna/String.h b/libluna/include/luna/String.h
index 6fd22e94..7b22c4ea 100644
--- a/libluna/include/luna/String.h
+++ b/libluna/include/luna/String.h
@@ -1,6 +1,7 @@
 #pragma once
 #include <luna/Result.h>
 #include <luna/StringView.h>
+#include <stdarg.h>
 
 class String
 {
@@ -22,6 +23,9 @@ class String
 
     Result<String> substring(usize begin, usize size) const;
 
+    static Result<String> format(const String& fmt, ...);
+    static Result<String> format(StringView fmt, ...);
+
     static Result<String> from_cstring(const char* str);
 
     const char* chars() const
@@ -75,4 +79,6 @@ class String
     bool m_inline { true };
 
     usize m_length { 0 };
+
+    static Result<String> vformat(StringView fmt, va_list ap);
 };
diff --git a/libluna/include/luna/Units.h b/libluna/include/luna/Units.h
index 3872c7ac..dccc8010 100644
--- a/libluna/include/luna/Units.h
+++ b/libluna/include/luna/Units.h
@@ -2,5 +2,4 @@
 #include <luna/Result.h>
 #include <luna/String.h>
 
-usize to_dynamic_unit_cstr(usize value, char* buffer, usize max);
 Result<String> to_dynamic_unit(usize value);
diff --git a/libluna/src/String.cpp b/libluna/src/String.cpp
index ec99bde1..3d0fc465 100644
--- a/libluna/src/String.cpp
+++ b/libluna/src/String.cpp
@@ -1,6 +1,8 @@
 #include <luna/Alloc.h>
 #include <luna/CString.h>
+#include <luna/Format.h>
 #include <luna/String.h>
+#include <luna/Vector.h>
 
 String::String()
 {
@@ -61,6 +63,43 @@ const char& String::operator[](usize index) const
     return chars()[index];
 }
 
+Result<String> String::format(const String& fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+
+    auto rc = vformat(fmt.view(), ap);
+
+    va_end(ap);
+
+    return rc;
+}
+
+Result<String> String::format(StringView fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+
+    auto rc = vformat(fmt, ap);
+
+    va_end(ap);
+
+    return rc;
+}
+
+Result<String> String::vformat(StringView fmt, va_list ap)
+{
+    Vector<char> buf;
+
+    TRY(cstyle_format(
+        fmt.chars(), [](char c, void* data) -> Result<void> { return ((Vector<char>*)data)->try_append(c); }, &buf,
+        ap));
+
+    TRY(buf.try_append(0));
+
+    return from_cstring(buf.data());
+}
+
 Result<String> String::from_cstring(const char* str)
 {
     usize len = strlen(str);
diff --git a/libluna/src/Units.cpp b/libluna/src/Units.cpp
index 19e79847..fd05f853 100644
--- a/libluna/src/Units.cpp
+++ b/libluna/src/Units.cpp
@@ -1,12 +1,11 @@
 #include <luna/Alloc.h>
-#include <luna/Format.h>
 #include <luna/Result.h>
 #include <luna/ScopeGuard.h>
 #include <luna/Units.h>
 
-usize to_dynamic_unit_cstr(usize value, char* buffer, usize max)
+Result<String> to_dynamic_unit(usize value)
 {
-    if (value < 1024) { return string_format(buffer, max, "%zu bytes", value); }
+    if (value < 1024) { return String::format("%zu bytes"_sv, value); }
 
     const char* unit_prefixes = "KMGTPE";
     while (value > (1024 * 1024))
@@ -15,14 +14,5 @@ usize to_dynamic_unit_cstr(usize value, char* buffer, usize max)
         unit_prefixes++;
     }
 
-    return string_format(buffer, max, "%zu.%zu %ciB", value / 1024, (value % 1024) / 103, *unit_prefixes);
-}
-
-Result<String> to_dynamic_unit(usize value)
-{
-    char* const buf = TRY(make_array<char>(64));
-
-    to_dynamic_unit_cstr(value, buf, 64);
-
-    return String { buf };
+    return String::format("%zu.%zu %ciB"_sv, value / 1024, (value % 1024) / 103, *unit_prefixes);
 }