diff --git a/Makefile b/Makefile
index 0f269f7..a21b126 100644
--- a/Makefile
+++ b/Makefile
@@ -17,7 +17,7 @@ CC=cc
 RUSTC=rustc
 
 .PHONY: all
-all: dj false fop intcmp rpn scrut str strcmp true
+all: dj false fop hru intcmp rpn scrut str strcmp true
 
 build:
 	# keep build/include until bindgen(1) has stdin support
@@ -74,6 +74,13 @@ build/bin/fop: src/fop.rs build build/o/libgetopt.rlib build/o/libsysexits.rlib
 		--extern sysexits=build/o/libsysexits.rlib \
 		-o $@ src/fop.rs
 
+.PHONY: hru
+hru: build/bin/hru
+build/bin/hru: src/hru.rs build build/o/libgetopt.rlib build/o/libsysexits.rlib
+	$(RUSTC) $(RUSTFLAGS) --extern getopt=build/o/libgetopt.rlib \
+		--extern sysexits=build/o/libsysexits.rlib \
+		-o $@ src/hru.rs
+
 .PHONY: intcmp
 intcmp: build/bin/intcmp
 build/bin/intcmp: src/intcmp.c build
diff --git a/src/hru.rs b/src/hru.rs
new file mode 100644
index 0000000..c7b88af
--- /dev/null
+++ b/src/hru.rs
@@ -0,0 +1,110 @@
+/*
+ * Copyright (c) 2023 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Affero General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see https://www.gnu.org/licenses/.
+ */
+
+use std::{
+	cmp::Ordering,
+	env::args,
+	io::stdin,
+	process::exit,
+};
+
+extern crate sysexits;
+
+use sysexits::EX_SOFTWARE;
+
+fn auto_c(input: u64) -> (u64, u32) {
+	let mut number = input;
+	let mut remainder = 0;
+	let mut exp: u32 = 0;
+
+	if number % 10 > 0 { }
+	else {
+		while remainder == 0 {
+			number /= 10;
+			remainder = number % 10;
+			exp += 1;
+		}
+	}
+
+	let list: Vec<u32> = vec![3, 6, 9, 12, 15, 18, 21, 24, 27, 30];
+	let mut exps = list.iter().peekable();
+
+	while let Some(i) = exps.next() {
+		match exp.cmp(i) {
+			Ordering::Less => {
+				number = input;
+				break;
+			},
+			Ordering::Equal => break,
+			Ordering::Greater => {
+				if let Some(p) = exps.peek() {
+					match exp.cmp(p) {
+						Ordering::Less => {
+							let exp_e = 10_u64.checked_pow(exp)
+								.unwrap_or_else(|| { exit(EX_SOFTWARE); });
+
+							let index_e = 10_u64.checked_pow(i.to_owned())
+								.unwrap_or_else(|| { exit(EX_SOFTWARE); });
+
+							number *= exp_e / index_e;
+							exp = *i;
+							break;
+						},
+						Ordering::Greater => continue,
+						_ => break,
+					};
+				}
+			},
+		};
+	}
+
+	(number, exp)
+}
+
+
+fn main() {
+	let argv = args().collect::<Vec<String>>();
+	let mut buf = String::new();
+	let _ = stdin().read_line(&mut buf);
+
+	let n: u64 = match buf.trim().parse() {
+		Ok(f) => f,
+		Err(err) => {
+			eprintln!("{}: {}", argv[0], err);
+			exit(1);
+		},
+	};
+
+	let (number, prefix) = auto_c(n);
+
+	let si_prefix = format!("{}B", match prefix {
+		3 => "K",
+		6 => "M",
+		9 => "G",
+		12 => "T",
+		15 => "P",
+		18 => "E",
+		21 => "Z",
+		24 => "Y",
+		27 => "R",
+		30 => "Q",
+		_ => "",
+	});
+
+	println!("{} {}", number.to_string(), si_prefix);
+}