diff --git a/Cargo.lock b/Cargo.lock
index 737d21ab..11c1fc3d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -7,6 +7,7 @@ dependencies = [
  "libc 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "mio 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "number_prefix 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "protobuf 1.0.20 (registry+https://github.com/rust-lang/crates.io-index)",
  "retry 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempdir 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -142,6 +143,80 @@ dependencies = [
  "libc 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "num"
+version = "0.1.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num-bigint 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-complex 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-integer 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-iter 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-rational 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-traits 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "num-bigint"
+version = "0.1.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num-integer 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-traits 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-serialize 0.3.19 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "num-complex"
+version = "0.1.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num-traits 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-serialize 0.3.19 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "num-integer"
+version = "0.1.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num-traits 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "num-iter"
+version = "0.1.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num-integer 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-traits 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "num-rational"
+version = "0.1.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num-bigint 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-integer 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-traits 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-serialize 0.3.19 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.1.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "number_prefix"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "protobuf"
 version = "1.0.20"
@@ -180,6 +255,11 @@ dependencies = [
  "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "rustc-serialize"
+version = "0.3.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "slab"
 version = "0.1.3"
diff --git a/Cargo.toml b/Cargo.toml
index 2c4342b2..c61521b5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,6 +9,7 @@ env_logger = "0.3.3"
 libc = "0.2.10"
 log = "0.3.6"
 mio = "0.5"
+number_prefix = "0.2.5"
 protobuf = "1.0.18"
 retry = "0.4.0"
 tempdir = "0.3.4"
diff --git a/src/commands.rs b/src/commands.rs
index 11b0ebe6..562c3820 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -22,6 +22,7 @@ use mock_command::{
     CommandCreatorSync,
     ProcessCommandCreator,
 };
+use number_prefix::{binary_prefix, Standalone, Prefixed};
 use protobuf::RepeatedField;
 use protocol::{
     CacheStats,
@@ -129,29 +130,6 @@ pub fn request_shutdown(mut conn : ServerConnection) -> io::Result<CacheStats> {
     }
 }
 
-/// Format `size_in_bytes` as a size in sensible units.
-///
-/// e.g. format_size(3 * 1024 * 1024 * 1024) == "3 GB"
-fn format_size(size_in_bytes : u64) -> String {
-    let mut size = size_in_bytes;
-    let mut remainder = 0;
-    for suffix in ["bytes", "kB", "MB", "GB", "TB"].iter() {
-        if size < 1024 {
-            let frac = if remainder > 0 {
-                let rem = (100.0 * remainder as f32 / 1024.0).trunc() as i32;
-                format!(".{}", if rem % 10 == 0 { rem / 10 } else { rem })
-            } else {
-                "".to_owned()
-            };
-            return format!("{}{} {}", size, frac, suffix);
-        }
-        remainder = size % 1024;
-        size = size / 1024;
-    }
-    //TODO: handle this more gracefully
-    return format!("{} {}", size, "PB");
-}
-
 /// Print `stats` to stdout.
 fn print_stats(stats : CacheStats) -> io::Result<()> {
     for stat in stats.get_stats().iter() {
@@ -162,7 +140,10 @@ fn print_stats(stats : CacheStats) -> io::Result<()> {
         } else if stat.has_str() {
             print!("{}", stat.get_str());
         } else if stat.has_size() {
-            print!("{}", format_size(stat.get_size()));
+            match binary_prefix(stat.get_size() as f64) {
+                Standalone(bytes) => print!("{} bytes", bytes),
+                Prefixed(prefix, n) => print!("{:.0} {}B", n, prefix),
+            }
         }
         print!("\n");
     }
@@ -321,23 +302,3 @@ pub fn run_command(cmd : Command) -> i32 {
         },
     }
 }
-
-#[cfg(test)]
-mod test {
-    use super::format_size;
-
-    #[test]
-    fn test_format_size() {
-        assert_eq!("10 bytes", format_size(10));
-        assert_eq!("1023 bytes", format_size(1023));
-        assert_eq!("1 kB", format_size(1024));
-        assert_eq!("1.5 kB", format_size(1024 + 512));
-        assert_eq!("1023.99 kB", format_size(1024 * 1024 - 1));
-        assert_eq!("1 MB", format_size(1024 * 1024));
-        assert_eq!("1 GB", format_size(1024 * 1024 * 1024));
-        assert_eq!("1.25 GB", format_size(1024 * 1024 * (1024 + 256)));
-        assert_eq!("3 GB", format_size(1024 * 1024 * 1024 * 3));
-        assert_eq!("1 TB", format_size(1024 * 1024 * 1024 * 1024));
-        assert_eq!("1 PB", format_size(1024 * 1024 * 1024 * 1024 * 1024));
-    }
-}
diff --git a/src/main.rs b/src/main.rs
index 16fbfa38..b8286304 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -17,6 +17,7 @@ extern crate env_logger;
 #[macro_use] extern crate log;
 extern crate libc;
 extern crate mio;
+extern crate number_prefix;
 extern crate protobuf;
 extern crate retry;
 extern crate tempdir;