diff --git a/docs/cli.md b/docs/cli.md
index 2b954c8..6eaea93 100644
--- a/docs/cli.md
+++ b/docs/cli.md
@@ -22,7 +22,7 @@ With no file, ink reads stdin when something is piped in and opens the file brow
 | Option | What it does |
 |---|---|
 | `-t`, `--theme <THEME>` | Color theme. Default `auto`, which matches the terminal background. See [Themes](themes.md). |
-| `-w`, `--width <WIDTH>` | Max text width: 20 to 1000 columns, or `narrow`, `wide`, `full` |
+| `-w`, `--width <WIDTH>` | Max text width: 20 to 1000 columns, or `narrow` (60), `wide` (100), `full`. In the reader, explicit widths are limited only by the document pane; `full` uses the entire pane with two-column margins. Without a CLI or config width, text remains capped at 120 columns. |
 | `-s`, `--slides` | Presentation mode, split on `---` |
 | `-p`, `--plain` | Print rendered output instead of opening the reader. Automatic when stdout isn't a terminal. |
 | `--color <WHEN>` | `auto`, `always` or `never`. Default `auto`. See [Color in plain output](#color-in-plain-output). |
diff --git a/src/app.rs b/src/app.rs
index 6f158c6..5c1241d 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -2376,8 +2376,12 @@ fn build_tab(
     // Content must fit within the terminal even after the left margin, so cap
     // it at term_width - 4 (a requested --width wider than the terminal would
     // otherwise overflow and be clipped at the right edge).
-    let hard_cap = term_width.saturating_sub(4).clamp(8, 120);
-    let max_content_width = args.width.unwrap_or(hard_cap).clamp(8, hard_cap);
+    let available_width = term_width.saturating_sub(4).max(8);
+    let max_content_width = if args.full_width {
+        available_width
+    } else {
+        args.width.unwrap_or(120).clamp(8, available_width)
+    };
     let center_margin = if term_width > max_content_width + 4 {
         ((term_width - max_content_width) / 2) as usize
     } else {
@@ -2843,6 +2847,7 @@ mod section_tests {
             inputs: Vec::new(),
             theme: "dark".into(),
             width: None,
+            full_width: false,
             slides: false,
             plain: false,
             watch: false,
@@ -3079,6 +3084,62 @@ mod section_tests {
         assert_eq!(not_editable(&t), None);
     }
 
+    #[test]
+    fn full_width_uses_the_document_pane_with_small_margins() {
+        let graphics = crate::graphics::Graphics::halfblocks();
+        let source = "word ".repeat(300);
+        for terminal_width in [80, 200, 320] {
+            for toc_visible in [false, true] {
+                let mut args = test_args();
+                args.full_width = true;
+                args.width = Some(60); // A configured width must not limit full-width mode.
+                args.toc = toc_visible;
+                let pane_width = effective_width(terminal_width, toc_visible);
+                let tab = build_tab(source.as_str(), "t.md", &args, pane_width, 0, &graphics);
+                let lines: Vec<_> = tab.plain.iter().filter(|line| !line.is_empty()).collect();
+                assert!(lines.iter().all(|line| line.starts_with("  word")));
+                assert!(lines
+                    .iter()
+                    .all(|line| line.len() <= pane_width as usize - 2));
+                // Word wrapping may leave up to four unused columns.
+                assert!(lines[0].len() >= pane_width as usize - 6);
+            }
+        }
+    }
+
+    #[test]
+    fn requested_width_is_centered_and_clamped_to_the_document_pane() {
+        let graphics = crate::graphics::Graphics::halfblocks();
+        let source = "word ".repeat(300);
+        for (requested, terminal_width, margin, content_width) in [
+            (60, 200, 70, 60),
+            (120, 200, 40, 120),
+            (140, 200, 30, 140),
+            (160, 240, 40, 160),
+            (1000, 200, 2, 196),
+            (140, 80, 2, 76),
+        ] {
+            let mut args = test_args();
+            args.width = Some(requested);
+            let tab = build_tab(source.as_str(), "t.md", &args, terminal_width, 0, &graphics);
+            let first = tab.plain.iter().find(|line| !line.is_empty()).unwrap();
+            assert_eq!(first.len() - first.trim_start().len(), margin);
+            assert!(first.trim_start().len() <= content_width);
+            assert!(first.trim_start().len() >= content_width - 4);
+        }
+    }
+
+    #[test]
+    fn automatic_width_keeps_the_existing_reading_width() {
+        let graphics = crate::graphics::Graphics::halfblocks();
+        let source = "word ".repeat(300);
+        let tab = build_tab(source.as_str(), "t.md", &test_args(), 200, 0, &graphics);
+        let first = tab.plain.iter().find(|line| !line.is_empty()).unwrap();
+        assert_eq!(first.len() - first.trim_start().len(), 40);
+        assert!(first.trim_start().len() <= 120);
+        assert!(first.trim_start().len() >= 116);
+    }
+
     // The three ways a tab is rebuilt (re-layout, `--watch`, reload after
     // `e`) share `reload_tab`: the same state carried over and one clamp
     // rule. `rebuild_tab` used to clamp to `len - 1`, leaving a mostly
diff --git a/src/cli.rs b/src/cli.rs
index af4880a..a10f977 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -205,6 +205,8 @@ pub struct Args {
     pub inputs: Vec<String>,
     pub theme: String,
     pub width: Option<u16>,
+    /// Use the entire document pane in the interactive reader.
+    pub full_width: bool,
     pub slides: bool,
     pub plain: bool,
     pub watch: bool,
@@ -367,6 +369,7 @@ pub fn run() -> Result<()> {
         inputs,
         theme,
         width,
+        full_width: cli.width == Some(WidthArg::Full),
         slides: cli.slides,
         // The interactive reader needs a terminal: with stdout piped or
         // redirected (`ink file.md | cat`), render plain output instead.
diff --git a/tests/cli.rs b/tests/cli.rs
index e886231..8aea32a 100644
--- a/tests/cli.rs
+++ b/tests/cli.rs
@@ -361,6 +361,22 @@ fn documented_flag_values_still_work() {
     }
 }
 
+#[test]
+fn full_width_keeps_the_existing_plain_output_width() {
+    let source = "word ".repeat(100);
+    let render = |width| {
+        ink()
+            .args(["--plain", "--color=never", "--theme=dark", "-w", width])
+            .write_stdin(source.as_str())
+            .assert()
+            .success()
+            .get_output()
+            .stdout
+            .clone()
+    };
+    assert_eq!(render("full"), render("80"));
+}
+
 #[test]
 fn config_syntax_error_warns_and_ink_still_runs() {
     let dir = xdg_with_config("theme = \"nord\"\nwidth = \n");
diff --git a/tests/mermaid.rs b/tests/mermaid.rs
index 3f80e1c..b644fdd 100644
--- a/tests/mermaid.rs
+++ b/tests/mermaid.rs
@@ -9,6 +9,7 @@ fn args(width: u16) -> Args {
         inputs: vec![],
         theme: "dark".to_string(),
         width: Some(width),
+        full_width: false,
         slides: false,
         plain: true,
         watch: false,
diff --git a/tests/plain_snapshots.rs b/tests/plain_snapshots.rs
index 80c043b..421e24d 100644
--- a/tests/plain_snapshots.rs
+++ b/tests/plain_snapshots.rs
@@ -12,6 +12,7 @@ fn test_args() -> Args {
         inputs: vec![],
         theme: "dark".to_string(),
         width: Some(80),
+        full_width: false,
         slides: false,
         plain: true,
         watch: false,
diff --git a/tests/pty.rs b/tests/pty.rs
index 256de13..6e5fa6f 100644
--- a/tests/pty.rs
+++ b/tests/pty.rs
@@ -27,15 +27,18 @@ fn run_in_pty(
     envs: &[(&str, &str)],
     mut respond: impl FnMut(&[u8], Duration) -> Option<Vec<u8>>,
 ) -> Session {
-    run_in_pty_ctl(args, envs, move |out, t| respond(out, t).map(Reply::Type))
+    run_in_pty_ctl(args, envs, 100, move |out, t| {
+        respond(out, t).map(Reply::Type)
+    })
 }
 
 fn run_in_pty_ctl(
     args: &[&str],
     envs: &[(&str, &str)],
+    width: u16,
     mut respond: impl FnMut(&[u8], Duration) -> Option<Reply>,
 ) -> Session {
-    let (mut master, slave) = open_pty();
+    let (mut master, slave) = open_pty(width);
     let config_home = tempfile::tempdir().unwrap();
     // An `ink/` directory makes ink use this (empty) config instead of the
     // developer's real one.
@@ -114,11 +117,11 @@ fn run_in_pty_ctl(
     Session { output }
 }
 
-fn open_pty() -> (std::fs::File, OwnedFd) {
+fn open_pty(width: u16) -> (std::fs::File, OwnedFd) {
     let (mut m, mut s) = (0, 0);
     let mut size = libc::winsize {
         ws_row: 30,
-        ws_col: 100,
+        ws_col: width,
         ws_xpixel: 0,
         ws_ypixel: 0,
     };
@@ -558,6 +561,35 @@ fn reader_args(path: &std::path::Path) -> Vec<String> {
     .collect()
 }
 
+#[test]
+fn explicit_width_is_honored_on_a_wide_terminal() {
+    let doc = tempfile::Builder::new().suffix(".md").tempfile().unwrap();
+    std::fs::write(doc.path(), "x".repeat(600)).unwrap();
+    for (width, expected) in [
+        (None, 120),
+        (Some("full"), 196),
+        (Some("120"), 120),
+        (Some("140"), 140),
+        (Some("1000"), 196),
+    ] {
+        let mut args = reader_args(doc.path());
+        if let Some(width) = width {
+            args.extend(["-w".into(), width.into()]);
+        }
+        let args: Vec<&str> = args.iter().map(String::as_str).collect();
+        let s = run_in_pty_ctl(&args, &[], 200, control_steps(Vec::new(), Marks::default()));
+        assert!(contains(&s.output, b"\x1b[?1049l"), "reader did not exit");
+        assert!(
+            contains(&s.output, "x".repeat(expected).as_bytes()),
+            "{width:?}"
+        );
+        assert!(
+            !contains(&s.output, "x".repeat(expected + 1).as_bytes()),
+            "{width:?}"
+        );
+    }
+}
+
 #[test]
 fn the_toc_takes_focus_filters_and_jumps() {
     let doc = long_doc_with_anchor_link();
@@ -597,7 +629,7 @@ fn shrinking_the_window_gives_focus_back_to_the_document() {
     ];
     let args = reader_args(doc.path());
     let args: Vec<&str> = args.iter().map(String::as_str).collect();
-    let s = run_in_pty_ctl(&args, &[], control_steps(steps, Marks::clone(&marks)));
+    let s = run_in_pty_ctl(&args, &[], 100, control_steps(steps, Marks::clone(&marks)));
     let marks = marks.borrow();
     assert_eq!(marks.len(), 3, "steps not all sent");
     let focused = String::from_utf8_lossy(&s.output[marks[0]..marks[1]]);
diff --git a/tests/rendering_features.rs b/tests/rendering_features.rs
index 4e49c68..7c39717 100644
--- a/tests/rendering_features.rs
+++ b/tests/rendering_features.rs
@@ -10,6 +10,7 @@ fn args() -> Args {
         inputs: vec![],
         theme: "dark".to_string(),
         width: Some(80),
+        full_width: false,
         slides: false,
         plain: true,
         watch: false,
diff --git a/tests/security.rs b/tests/security.rs
index 96da4a1..bfedf3c 100644
--- a/tests/security.rs
+++ b/tests/security.rs
@@ -9,6 +9,7 @@ fn args() -> Args {
         inputs: vec![],
         theme: "dark".to_string(),
         width: Some(80),
+        full_width: false,
         slides: false,
         plain: true,
         watch: false,