diff --git a/src/ConsoleStatCalc.cc b/src/ConsoleStatCalc.cc
index a28a4a54..abd510b1 100644
--- a/src/ConsoleStatCalc.cc
+++ b/src/ConsoleStatCalc.cc
@@ -80,10 +80,15 @@ std::string SizeFormatter::operator()(int64_t size) const
 
 namespace {
 class AbbrevSizeFormatter : public SizeFormatter {
+private:
+  bool useSI_;
+
+public:
+  explicit AbbrevSizeFormatter(bool useSI) : useSI_{useSI} {}
 protected:
   virtual std::string format(int64_t size) const CXX11_OVERRIDE
   {
-    return util::abbrevSize(size);
+    return util::abbrevSize(size, useSI_);
   }
 };
 } // namespace
@@ -267,7 +272,7 @@ void printProgressSummary(const RequestGroupList& groups, size_t cols,
 }
 } // namespace
 
-ConsoleStatCalc::ConsoleStatCalc(std::chrono::seconds summaryInterval,
+ConsoleStatCalc::ConsoleStatCalc(std::chrono::seconds summaryInterval, bool useSI,
                                  bool colorOutput, bool humanReadable)
     : summaryInterval_(std::move(summaryInterval)),
       readoutVisibility_(true),
@@ -278,9 +283,10 @@ ConsoleStatCalc::ConsoleStatCalc(std::chrono::seconds summaryInterval,
       isTTY_(isatty(STDOUT_FILENO) == 1),
 #endif // !__MINGW32__
       colorOutput_(colorOutput)
-{
+{ 
+
   if (humanReadable) {
-    sizeFormatter_ = make_unique<AbbrevSizeFormatter>();
+    sizeFormatter_ = make_unique<AbbrevSizeFormatter>(useSI);
   }
   else {
     sizeFormatter_ = make_unique<PlainSizeFormatter>();
diff --git a/src/ConsoleStatCalc.h b/src/ConsoleStatCalc.h
index 76bfd5b7..09a979b5 100644
--- a/src/ConsoleStatCalc.h
+++ b/src/ConsoleStatCalc.h
@@ -35,6 +35,7 @@
 #ifndef D_CONSOLE_STAT_CALC_H
 #define D_CONSOLE_STAT_CALC_H
 
+#include "Option.h"
 #include "StatCalc.h"
 
 #include <string>
@@ -70,8 +71,8 @@ private:
   bool colorOutput_;
 
 public:
-  ConsoleStatCalc(std::chrono::seconds summaryInterval, bool colorOutput = true,
-                  bool humanReadable = true);
+  ConsoleStatCalc(std::chrono::seconds summaryInterval, bool useSI = false,
+                  bool colorOutput = true, bool humanReadable = true);
 
   virtual ~ConsoleStatCalc() = default;
 
diff --git a/src/MultiUrlRequestInfo.cc b/src/MultiUrlRequestInfo.cc
index 46396f9c..84d81ac9 100644
--- a/src/MultiUrlRequestInfo.cc
+++ b/src/MultiUrlRequestInfo.cc
@@ -137,6 +137,7 @@ std::unique_ptr<StatCalc> getStatCalc(const std::shared_ptr<Option>& op)
   }
   auto impl = make_unique<ConsoleStatCalc>(
       std::chrono::seconds(op->getAsInt(PREF_SUMMARY_INTERVAL)),
+      op->getAsBool(PREF_USE_SI_UNITS),
       op->getAsBool(PREF_ENABLE_COLOR), op->getAsBool(PREF_HUMAN_READABLE));
   impl->setReadoutVisibility(op->getAsBool(PREF_SHOW_CONSOLE_READOUT));
   impl->setTruncate(op->getAsBool(PREF_TRUNCATE_CONSOLE_READOUT));
diff --git a/src/OptionHandlerFactory.cc b/src/OptionHandlerFactory.cc
index 000426b6..a6ff2ec1 100644
--- a/src/OptionHandlerFactory.cc
+++ b/src/OptionHandlerFactory.cc
@@ -1993,6 +1993,16 @@ std::vector<OptionHandler*> OptionHandlerFactory::createOptionHandlers()
     handlers.push_back(op);
   }
 
+  // SI units option
+  {
+    OptionHandler* op(
+        new BooleanOptionHandler(PREF_USE_SI_UNITS, TEXT_USE_SI_UNITS,
+                                 A2_V_FALSE, OptionHandler::NO_ARG));
+    op->addTag(TAG_BASIC);
+    op->setInitialOption(true);
+    op->setChangeGlobalOption(true);
+    handlers.push_back(op);
+  }
   return handlers;
 }
 
diff --git a/src/RequestGroupMan.cc b/src/RequestGroupMan.cc
index 425351bb..6e8e7829 100644
--- a/src/RequestGroupMan.cc
+++ b/src/RequestGroupMan.cc
@@ -85,6 +85,7 @@
 #include "OpenedFileCounter.h"
 #include "wallclock.h"
 #include "RpcMethodImpl.h"
+
 #ifdef ENABLE_BITTORRENT
 #  include "bittorrent_helper.h"
 #endif // ENABLE_BITTORRENT
@@ -714,6 +715,7 @@ void RequestGroupMan::showDownloadResults(OutputFile& o, bool full) const
   std::string line(pathRowSize, '=');
   o.printf("%s\n", line.c_str());
   bool useColor = o.supportsColor() && option_->getAsBool(PREF_ENABLE_COLOR);
+  bool useSI = option_->getAsBool(PREF_USE_SI_UNITS);
   int ok = 0;
   int err = 0;
   int inpr = 0;
@@ -742,10 +744,10 @@ void RequestGroupMan::showDownloadResults(OutputFile& o, bool full) const
       ++err;
     }
     if (full) {
-      formatDownloadResultFull(o, status, dr);
+      formatDownloadResultFull(o, status, dr, useSI);
     }
     else {
-      o.write(formatDownloadResult(status, dr).c_str());
+      o.write(formatDownloadResult(status, dr, useSI).c_str());
       o.write("\n");
     }
   }
@@ -770,14 +772,15 @@ void RequestGroupMan::showDownloadResults(OutputFile& o, bool full) const
 namespace {
 void formatDownloadResultCommon(
     std::ostream& o, const char* status,
-    const std::shared_ptr<DownloadResult>& downloadResult)
+    const std::shared_ptr<DownloadResult>& downloadResult,
+    bool useSI)
 {
   o << std::setw(3) << downloadResult->gid->toAbbrevHex() << "|" << std::setw(4)
     << status << "|";
   if (downloadResult->sessionTime.count() > 0) {
     o << std::setw(8)
       << util::abbrevSize(downloadResult->sessionDownloadLength * 1000 /
-                          downloadResult->sessionTime.count())
+                          downloadResult->sessionTime.count(), useSI)
       << "B/s";
   }
   else {
@@ -790,7 +793,8 @@ void formatDownloadResultCommon(
 
 void RequestGroupMan::formatDownloadResultFull(
     OutputFile& out, const char* status,
-    const std::shared_ptr<DownloadResult>& downloadResult) const
+    const std::shared_ptr<DownloadResult>& downloadResult,
+    bool useSI) const
 {
   BitfieldMan bt(downloadResult->pieceLength, downloadResult->totalLength);
   bt.setBitfield(
@@ -805,7 +809,7 @@ void RequestGroupMan::formatDownloadResultFull(
     }
     std::stringstream o;
     if (head) {
-      formatDownloadResultCommon(o, status, downloadResult);
+      formatDownloadResultCommon(o, status, downloadResult, useSI);
       head = false;
     }
     else {
@@ -825,7 +829,7 @@ void RequestGroupMan::formatDownloadResultFull(
   }
   if (head) {
     std::stringstream o;
-    formatDownloadResultCommon(o, status, downloadResult);
+    formatDownloadResultCommon(o, status, downloadResult, useSI);
     o << "  -|n/a\n";
     out.write(o.str().c_str());
   }
@@ -833,10 +837,11 @@ void RequestGroupMan::formatDownloadResultFull(
 
 std::string RequestGroupMan::formatDownloadResult(
     const char* status,
-    const std::shared_ptr<DownloadResult>& downloadResult) const
+    const std::shared_ptr<DownloadResult>& downloadResult,
+    bool useSI) const
 {
   std::stringstream o;
-  formatDownloadResultCommon(o, status, downloadResult);
+  formatDownloadResultCommon(o, status, downloadResult, useSI);
   const std::vector<std::shared_ptr<FileEntry>>& fileEntries =
       downloadResult->fileEntries;
   writeFilePath(fileEntries.begin(), fileEntries.end(), o,
@@ -1103,12 +1108,14 @@ int RequestGroupMan::optimizeConcurrentDownloads()
   maxConcurrentDownloads =
       std::min(std::max(1, maxConcurrentDownloads), maxConcurrentDownloads_);
 
+  bool useSI = option_->getAsBool(PREF_USE_SI_UNITS);
+
   A2_LOG_DEBUG(
       fmt("Max concurrent downloads optimized at %d (%lu currently active) "
           "[optimization speed %sB/s, current speed %sB/s]",
           maxConcurrentDownloads, static_cast<unsigned long>(numActive_),
-          util::abbrevSize(optimizationSpeed_).c_str(),
-          util::abbrevSize(currentSpeed).c_str()));
+          util::abbrevSize(optimizationSpeed_, useSI).c_str(),
+          util::abbrevSize(currentSpeed, useSI).c_str()));
 
   return maxConcurrentDownloads;
 }
diff --git a/src/RequestGroupMan.h b/src/RequestGroupMan.h
index b8aa8d4f..12ddd31f 100644
--- a/src/RequestGroupMan.h
+++ b/src/RequestGroupMan.h
@@ -132,11 +132,13 @@ private:
 
   void formatDownloadResultFull(
       OutputFile& out, const char* status,
-      const std::shared_ptr<DownloadResult>& downloadResult) const;
+      const std::shared_ptr<DownloadResult>& downloadResult,
+      bool useSI = false) const;
 
-  std::string formatDownloadResult(
-      const char* status,
-      const std::shared_ptr<DownloadResult>& downloadResult) const;
+  std::string
+  formatDownloadResult(const char* status,
+                       const std::shared_ptr<DownloadResult>& downloadResult,
+                       bool useSI = false) const;
 
   void configureRequestGroup(
       const std::shared_ptr<RequestGroup>& requestGroup) const;
diff --git a/src/prefs.cc b/src/prefs.cc
index 2591b9f0..64855ab9 100644
--- a/src/prefs.cc
+++ b/src/prefs.cc
@@ -592,4 +592,10 @@ PrefPtr PREF_METALINK_ENABLE_UNIQUE_PROTOCOL =
     makePref("metalink-enable-unique-protocol");
 PrefPtr PREF_METALINK_BASE_URI = makePref("metalink-base-uri");
 
+/**
+ * Units related (IEC/SI)
+ */
+// values: true | false
+PrefPtr PREF_USE_SI_UNITS = makePref("si-units");
+
 } // namespace aria2
diff --git a/src/prefs.h b/src/prefs.h
index 338fd6e6..97bb2dcf 100644
--- a/src/prefs.h
+++ b/src/prefs.h
@@ -542,6 +542,12 @@ extern PrefPtr PREF_METALINK_ENABLE_UNIQUE_PROTOCOL;
 // values: a string
 extern PrefPtr PREF_METALINK_BASE_URI;
 
+/**
+ * Units related (IEC/SI)
+ */
+// values: true | false
+extern PrefPtr PREF_USE_SI_UNITS;
+
 } // namespace aria2
 
 #endif // D_PREFS_H
diff --git a/src/usage_text.h b/src/usage_text.h
index 08715436..19514aee 100644
--- a/src/usage_text.h
+++ b/src/usage_text.h
@@ -1129,5 +1129,8 @@
     "                              file saved by --bt-save-metadata option. If it is\n" \
     "                              successful, then skip downloading metadata from\n" \
     "                              DHT.")
+#define TEXT_USE_SI_UNITS \
+  _(" --si-units[=true|false]\n"\
+      "Use SI units (kB, MB, GB) instead of IEC units (KiB, MiB, GiB).")
 
 // clang-format on
diff --git a/src/util.cc b/src/util.cc
index 07502c0e..4c894f5c 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -1857,20 +1857,25 @@ int64_t getRealSize(const std::string& sizeWithUnit)
   return v * mult;
 }
 
-std::string abbrevSize(int64_t size)
+std::string abbrevSize(int64_t size, bool useSI)
 {
-  static const char* UNITS[] = {"", "Ki", "Mi", "Gi"};
+  static const char* IEC_UNITS[] = {"", "Ki", "Mi", "Gi"};
+  static const char* SI_UNITS[] = {"", "K", "M", "G"}; 
+
+  const char** units = useSI ? SI_UNITS : IEC_UNITS;
+  int64_t divisor = useSI ? 1000 : 1024;
+
   int64_t t = size;
   size_t uidx = 0;
   int r = 0;
-  while (t >= static_cast<int64_t>(1_k) &&
-         uidx + 1 < sizeof(UNITS) / sizeof(UNITS[0])) {
-    lldiv_t d = lldiv(t, 1_k);
+  while (t >= divisor &&
+        uidx + 1 < sizeof(units)) {
+    lldiv_t d = lldiv(t, divisor);
     t = d.quot;
     r = d.rem;
     ++uidx;
   }
-  if (uidx + 1 < sizeof(UNITS) / sizeof(UNITS[0]) && t >= 922) {
+  if (uidx + 1 < sizeof(units) && t >= 922) {
     ++uidx;
     r = t;
     t = 0;
@@ -1879,9 +1884,9 @@ std::string abbrevSize(int64_t size)
   res += itos(t, true);
   if (t < 10 && uidx > 0) {
     res += ".";
-    res += itos(r * 10 / 1_k);
+    res += itos(r * 10 / divisor);
   }
-  res += UNITS[uidx];
+  res += units[uidx];
   return res;
 }
 
diff --git a/src/util.h b/src/util.h
index bb7d8d3e..27c73d7e 100644
--- a/src/util.h
+++ b/src/util.h
@@ -361,7 +361,7 @@ std::string getDHTFile(bool ipv6);
 
 int64_t getRealSize(const std::string& sizeWithUnit);
 
-std::string abbrevSize(int64_t size);
+std::string abbrevSize(int64_t size, bool useSI = false);
 
 template <typename InputIterator, typename Output>
 void toStream(InputIterator first, InputIterator last, Output& os)