diff --git a/src/uu/numfmt/locales/en-US.ftl b/src/uu/numfmt/locales/en-US.ftl
index 14141b9cc7f..a2ad787bd2f 100644
--- a/src/uu/numfmt/locales/en-US.ftl
+++ b/src/uu/numfmt/locales/en-US.ftl
@@ -47,6 +47,7 @@ numfmt-help-padding = pad the output to N characters; positive N will right-alig
 numfmt-help-header = print (without converting) the first N header lines; N defaults to 1 if not specified
 numfmt-help-round = use METHOD for rounding when scaling
 numfmt-help-suffix = print SUFFIX after each formatted number, and accept inputs optionally ending with SUFFIX
+numfmt-help-unit-separator = use STRING to separate the number from any unit when printing; by default, no separator is used
 numfmt-help-invalid = set the failure mode for invalid input
 numfmt-help-zero-terminated = line delimiter is NUL, not newline
 
diff --git a/src/uu/numfmt/src/format.rs b/src/uu/numfmt/src/format.rs
index e091f232079..33dc58bc29d 100644
--- a/src/uu/numfmt/src/format.rs
+++ b/src/uu/numfmt/src/format.rs
@@ -275,6 +275,7 @@ fn transform_to(
     opts: &TransformOptions,
     round_method: RoundMethod,
     precision: usize,
+    unit_separator: &str,
 ) -> Result<String> {
     let (i2, s) = consider_suffix(s, &opts.to, round_method, precision)?;
     let i2 = i2 / (opts.to_unit as f64);
@@ -286,10 +287,15 @@ fn transform_to(
             )
         }
         Some(s) if precision > 0 => {
-            format!("{i2:.precision$}{}", DisplayableSuffix(s, opts.to),)
+            format!(
+                "{i2:.precision$}{unit_separator}{}",
+                DisplayableSuffix(s, opts.to),
+            )
+        }
+        Some(s) if i2.abs() < 10.0 => {
+            format!("{i2:.1}{unit_separator}{}", DisplayableSuffix(s, opts.to))
         }
-        Some(s) if i2.abs() < 10.0 => format!("{i2:.1}{}", DisplayableSuffix(s, opts.to)),
-        Some(s) => format!("{i2:.0}{}", DisplayableSuffix(s, opts.to)),
+        Some(s) => format!("{i2:.0}{unit_separator}{}", DisplayableSuffix(s, opts.to)),
     })
 }
 
@@ -317,6 +323,7 @@ fn format_string(
         &options.transform,
         options.round,
         precision,
+        &options.unit_separator,
     )?;
 
     // bring back the suffix before applying padding
diff --git a/src/uu/numfmt/src/numfmt.rs b/src/uu/numfmt/src/numfmt.rs
index abeaca25698..81e8ab9cd0a 100644
--- a/src/uu/numfmt/src/numfmt.rs
+++ b/src/uu/numfmt/src/numfmt.rs
@@ -234,6 +234,11 @@ fn parse_options(args: &ArgMatches) -> Result<NumfmtOptions> {
 
     let suffix = args.get_one::<String>(SUFFIX).cloned();
 
+    let unit_separator = args
+        .get_one::<String>(UNIT_SEPARATOR)
+        .cloned()
+        .unwrap_or_default();
+
     let invalid = InvalidModes::from_str(args.get_one::<String>(INVALID).unwrap()).unwrap();
 
     let zero_terminated = args.get_flag(ZERO_TERMINATED);
@@ -246,6 +251,7 @@ fn parse_options(args: &ArgMatches) -> Result<NumfmtOptions> {
         delimiter,
         round,
         suffix,
+        unit_separator,
         format,
         invalid,
         zero_terminated,
@@ -370,6 +376,12 @@ pub fn uu_app() -> Command {
                 .help(translate!("numfmt-help-suffix"))
                 .value_name("SUFFIX"),
         )
+        .arg(
+            Arg::new(UNIT_SEPARATOR)
+                .long(UNIT_SEPARATOR)
+                .help(translate!("numfmt-help-unit-separator"))
+                .value_name("STRING"),
+        )
         .arg(
             Arg::new(INVALID)
                 .long(INVALID)
@@ -419,6 +431,7 @@ mod tests {
             delimiter: None,
             round: RoundMethod::Nearest,
             suffix: None,
+            unit_separator: String::new(),
             format: FormatOptions::default(),
             invalid: InvalidModes::Abort,
             zero_terminated: false,
diff --git a/src/uu/numfmt/src/options.rs b/src/uu/numfmt/src/options.rs
index 48f4a4dae0c..eaf0d8b8b48 100644
--- a/src/uu/numfmt/src/options.rs
+++ b/src/uu/numfmt/src/options.rs
@@ -27,6 +27,7 @@ pub const TO: &str = "to";
 pub const TO_DEFAULT: &str = "none";
 pub const TO_UNIT: &str = "to-unit";
 pub const TO_UNIT_DEFAULT: &str = "1";
+pub const UNIT_SEPARATOR: &str = "unit-separator";
 pub const ZERO_TERMINATED: &str = "zero-terminated";
 
 pub struct TransformOptions {
@@ -52,6 +53,7 @@ pub struct NumfmtOptions {
     pub delimiter: Option<String>,
     pub round: RoundMethod,
     pub suffix: Option<String>,
+    pub unit_separator: String,
     pub format: FormatOptions,
     pub invalid: InvalidModes,
     pub zero_terminated: bool,
diff --git a/tests/by-util/test_numfmt.rs b/tests/by-util/test_numfmt.rs
index d947833f7c7..610e84adb52 100644
--- a/tests/by-util/test_numfmt.rs
+++ b/tests/by-util/test_numfmt.rs
@@ -1115,3 +1115,16 @@ fn test_zero_terminated_embedded_newline() {
         // Newlines get replaced by a single space
         .stdout_is("1000 2000\x003000 4000\x00");
 }
+
+#[test]
+fn test_unit_separator() {
+    for (args, expected) in [
+        (&["--to=si", "--unit-separator= ", "1000"][..], "1.0 k\n"),
+        (&["--to=iec", "--unit-separator= ", "1024"], "1.0 K\n"),
+        (&["--to=iec-i", "--unit-separator= ", "2048"], "2.0 Ki\n"),
+        (&["--to=si", "--unit-separator=__", "1000"], "1.0__k\n"),
+        (&["--to=si", "--unit-separator= ", "500"], "500\n"), // no unit = no separator
+    ] {
+        new_ucmd!().args(args).succeeds().stdout_only(expected);
+    }
+}