diff --git a/src/format.rs b/src/format.rs
index fe425df..f4b1dc8 100644
--- a/src/format.rs
+++ b/src/format.rs
@@ -2,6 +2,7 @@ use libpt::bintols::split;
 
 pub type Num = u128;
 
+/// formats supported by numf
 #[derive(Copy, Clone, Debug)]
 pub enum Format {
     Dec,
@@ -12,6 +13,32 @@ pub enum Format {
     Base32,
 }
 
+/// Options to use when formatting a number
+///
+/// Used by [Format::format].
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub struct FormatOptions {
+    /// add a prefix to the formatted number, such as `0x` for hex
+    prefix: bool,
+    /// fill the formatted number with zeros (or the equivalent) to make a whole byte
+    padding: bool,
+}
+
+impl FormatOptions {
+    /// set prefix
+    pub fn prefix(mut self, value: bool) -> Self {
+        self.prefix = value;
+        self
+    }
+    /// set padding
+    ///
+    /// Does not apply to all formats
+    pub fn padding(mut self, value: bool) -> Self {
+        self.padding = value;
+        self
+    }
+}
+
 impl Format {
     pub fn prefix(&self) -> String {
         match self {
@@ -31,17 +58,27 @@ impl Format {
         }
         .to_string()
     }
-    pub fn format(&self, num: Num, prefix: bool) -> String {
+    pub fn format(&self, num: Num, options: FormatOptions) -> String {
         let mut buf = String::new();
-        if prefix {
+        if options.prefix {
             buf += &self.prefix();
         }
         match self {
             Format::Hex => {
-                buf += &format!("{num:X}");
+                if options.padding {
+                    let tmp = &format!("{num:X}");
+                    buf += &("0".repeat((2 - tmp.len() % 2) % 2) + tmp);
+                } else {
+                    buf += &format!("{num:X}");
+                }
             }
             Format::Bin => {
-                buf += &format!("{num:b}");
+                if options.padding {
+                    let tmp = &format!("{num:b}");
+                    buf += &("0".repeat((8 - tmp.len() % 8) % 8) + tmp);
+                } else {
+                    buf += &format!("{num:b}");
+                }
             }
             Format::Octal => {
                 buf += &format!("{num:o}");
diff --git a/src/main.rs b/src/main.rs
index 927ddfb..8559138 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -32,6 +32,12 @@ struct Cli {
     #[arg(short, long)]
     /// add a prefix (like "0x" for hex)
     prefix: bool,
+    #[arg(short = 'P', long)]
+    /// add a padding to make the number at least one byte long
+    ///
+    /// For example, `0b1100` will be `0b00001100` with this.
+    /// This does not apply to all formats, only hexadecimal and binary.
+    padding: bool,
     #[arg(short = 'x', long, default_value_t = true)]
     /// format to hexadecimal
     hex: bool,
@@ -79,11 +85,14 @@ impl Cli {
 
 fn main() {
     let cli = Cli::parse();
+    let options: FormatOptions = FormatOptions::default()
+        .padding(cli.padding)
+        .prefix(cli.prefix);
 
     let mut out: Vec<String> = Vec::new();
 
     for num in &cli.numbers {
-        out.push(cli.format().format(*num, cli.prefix));
+        out.push(cli.format().format(*num, options));
     }
     for o in out {
         println!("{o}")