diff --git a/config/dock/style.css b/config/dock/style.css.in
similarity index 66%
rename from config/dock/style.css
rename to config/dock/style.css.in
index e4769d5..037389e 100644
--- a/config/dock/style.css
+++ b/config/dock/style.css.in
@@ -1,3 +1,11 @@
+/* Ekklesia Classroom dock
+ *
+ * A template, not plain CSS. classroom-dock substitutes the bracketed
+ * measurements at startup from UI_SCALE in device.conf, so a room can
+ * be tuned for its TV without anyone editing this file. At UI_SCALE=1.0
+ * every token resolves to the value it had before scaling existed.
+ */
+
 window#classroom-dock,
 window#classroom-clock {
     background-color: transparent;
@@ -12,9 +20,9 @@ window#classroom-clock {
     background-color: rgba(34, 38, 50, 0.62);
 
     border: 1px solid rgba(255, 255, 255, 0.08);
-    border-radius: 24px;
+    border-radius: @dock-radius@px;
 
-    padding: 8px 10px;
+    padding: @dock-padding-v@px @dock-padding-h@px;
 
     /* Important: no shadow here.
        GTK was clipping it against the rectangular window edge. */
@@ -28,13 +36,13 @@ button.dock-button {
     background-color: rgba(255, 255, 255, 0.05);
 
     border: none;
-    border-radius: 16px;
+    border-radius: @button-radius@px;
 
-    padding: 6px;
+    padding: @button-padding@px;
     margin: 0;
 
-    min-width: 44px;
-    min-height: 44px;
+    min-width: @button-size@px;
+    min-height: @button-size@px;
 
     box-shadow: none;
     outline: none;
@@ -74,11 +82,11 @@ button.dock-button image {
     background-color: rgba(34, 38, 50, 0.62);
 
     border: 1px solid rgba(255, 255, 255, 0.08);
-    border-radius: 16px;
+    border-radius: @clock-radius@px;
 
-    padding: 7px 12px;
+    padding: @clock-padding-v@px @clock-padding-h@px;
 
-    font-size: 17px;
+    font-size: @clock-font@px;
     font-weight: 600;
 
     box-shadow: none;
diff --git a/config/mako/config b/config/mako/config.in
similarity index 62%
rename from config/mako/config
rename to config/mako/config.in
index d718a5e..b8cda50 100644
--- a/config/mako/config
+++ b/config/mako/config.in
@@ -4,8 +4,13 @@
 # Matched to the dock: same dark slate (#222632), same hairline white
 # border, same rounded corners, white text. Kept slightly more opaque
 # than the dock so text stays readable over the wallpaper and over video.
+#
+# A template, not a finished config. classroom-notifications resolves the
+# bracketed measurements from UI_SCALE in device.conf and starts mako on
+# the result. At UI_SCALE=1.0 they resolve to the values they had before
+# scaling existed.
 
-font=DejaVu Sans 12
+font=DejaVu Sans @font-size@
 
 background-color=#222632e6
 text-color=#ffffffff
@@ -13,13 +18,13 @@ border-color=#ffffff21
 progress-color=over #464b5ae6
 
 border-size=1
-border-radius=18
+border-radius=@radius@
 
-padding=14,18
-margin=18
+padding=@padding-v@,@padding-h@
+margin=@margin@
 
-width=380
-height=160
+width=@width@
+height=@height@
 
 anchor=top-right
 layer=overlay
@@ -30,7 +35,7 @@ markup=1
 format=<b>%s</b>\n%b
 
 icons=1
-max-icon-size=48
+max-icon-size=@icon-size@
 
 default-timeout=6000
 
diff --git a/config/sway/config b/config/sway/config
index 7fcbfbc..7c9771b 100644
--- a/config/sway/config
+++ b/config/sway/config
@@ -7,9 +7,9 @@ set $mod Mod4
 output * bg /usr/share/backgrounds/ekklesia/classroom-default.png fill
 
 # Notifications, started before the dock so nothing can race D-Bus into
-# activating an unstyled mako first. mako only ever searches ~/.config,
-# so the packaged config has to be named explicitly.
-exec --no-startup-id /usr/bin/mako --config /etc/ekklesia-classroom/mako/config
+# activating an unstyled mako first. The wrapper resolves the styling at
+# the room's UI scale and execs mako, so the process is still just mako.
+exec --no-startup-id /usr/local/bin/classroom-notifications
 
 # Ekklesia Classroom dock
 exec --no-startup-id /usr/local/bin/classroom-dock
diff --git a/docs/testing.md b/docs/testing.md
index f87058a..1e6225c 100644
--- a/docs/testing.md
+++ b/docs/testing.md
@@ -11,6 +11,17 @@ before promoting to stable with `./update_stable.sh`.
 - [ ] Dock appears, centred
 - [ ] Clock appears, bottom right
 
+## UI scale
+
+- [ ] `UI_SCALE=1.0` looks exactly as it did before scaling existed
+- [ ] `UI_SCALE=1.25`, then `sudo systemctl restart getty@tty1`:
+      dock, icons, clock and notifications all grow together
+- [ ] `UI_SCALE=0.8` shrinks them together
+- [ ] The reserved bottom strip grows and shrinks with the dock, and a
+      maximised Chrome window still stops above it
+- [ ] A nonsense value (`UI_SCALE=banana`) still gives a working shell
+- [ ] An extreme value (`UI_SCALE=9`) is clamped, not obeyed
+
 ## Reserved bottom shell (regression)
 
 The bottom strip is one full-width layer-shell surface with a 76px
diff --git a/docs/ui-scale.md b/docs/ui-scale.md
new file mode 100644
index 0000000..f752c0e
--- /dev/null
+++ b/docs/ui-scale.md
@@ -0,0 +1,60 @@
+# UI scale
+
+Every classroom gets the same design at a size that suits its TV. A 32"
+panel a few feet from the children and a 65" set across a hall want
+different sizes of the same dock, not different docks.
+
+## Changing it
+
+Edit `/etc/ekklesia-classroom/device.conf` on that endpoint:
+
+```
+UI_SCALE=1.25
+```
+
+Then restart the classroom shell:
+
+```
+sudo systemctl restart getty@tty1
+```
+
+That ends the session and the autologin brings it straight back with the
+new size. A reboot does the same thing. Nothing else needs touching, and
+no CSS or source file is ever edited to change a room's size.
+
+## Values
+
+| UI_SCALE | Roughly |
+| --- | --- |
+| 0.8 | Small or close-up panel |
+| 1.0 | Default. 1080p classroom TV, 32–50" |
+| 1.25 | Large room, or a set viewed from further back |
+| 1.5 | 65"+ |
+
+Anything outside 0.8–1.5 is clamped to that range, and anything that is
+not a number at all falls back to 1.0, so a typo in device.conf cannot
+produce an unusable shell.
+
+## What it scales
+
+- Dock height, and the reserved strip at the bottom of the screen
+- Dock corner radius, padding and the spacing between buttons
+- Button size, padding and corner radius
+- Every dock icon
+- Clock text size, padding, corner radius and its inset from the edge
+- Notification width, height, padding, margin, corner radius, text size
+  and icon size
+
+Colours, translucency and the hairline borders do not scale: those are
+the design, not the size. At `UI_SCALE=1.0` the rendered stylesheet is
+byte-identical to the one the shell used before scaling existed.
+
+## How it works
+
+`/etc/ekklesia-classroom/dock/style.css.in` and
+`/etc/ekklesia-classroom/mako/config.in` are templates carrying
+measurement tokens. `classroom-dock` resolves the stylesheet in memory at
+startup; `classroom-notifications` resolves the notification config into
+the session's runtime directory and hands it to mako. Neither template is
+ever rewritten on disk, so an update cannot lose a room's setting and a
+room's setting cannot drift from the packaged design.
diff --git a/lib/classroom_config.py b/lib/classroom_config.py
new file mode 100644
index 0000000..840d9bd
--- /dev/null
+++ b/lib/classroom_config.py
@@ -0,0 +1,65 @@
+"""Device configuration for the Ekklesia Classroom shell.
+
+Everything that has to agree about /etc/ekklesia-classroom/device.conf
+reads it through here, so the dock, the notification daemon and the DVD
+commands cannot drift apart over what a setting means.
+"""
+
+import math
+from pathlib import Path
+
+CONFIG_FILE = Path("/etc/ekklesia-classroom/device.conf")
+
+TRUTHY = {"1", "true", "yes", "on", "enabled"}
+
+# The dock is tuned for a 1080p classroom TV at 1.0. Smaller rooms with a
+# 32" panel sit near the bottom of this range, a 65" set near the top.
+UI_SCALE_DEFAULT = 1.0
+UI_SCALE_MIN = 0.8
+UI_SCALE_MAX = 1.5
+
+
+def read_device_config(path=None):
+    config = {}
+    path = Path(path) if path is not None else CONFIG_FILE
+
+    if not path.exists():
+        return config
+
+    for raw_line in path.read_text().splitlines():
+        line = raw_line.strip()
+
+        if not line or line.startswith("#") or "=" not in line:
+            continue
+
+        key, value = line.split("=", 1)
+        config[key.strip()] = value.strip()
+
+    return config
+
+
+def enabled(config, key, default=False):
+    if key not in config:
+        return default
+
+    return config[key].lower() in TRUTHY
+
+
+def ui_scale(config):
+    """UI_SCALE, clamped to something a classroom can actually use."""
+    raw = config.get("UI_SCALE", "")
+
+    try:
+        value = float(raw)
+    except (TypeError, ValueError):
+        return UI_SCALE_DEFAULT
+
+    if not math.isfinite(value):
+        return UI_SCALE_DEFAULT
+
+    return min(max(value, UI_SCALE_MIN), UI_SCALE_MAX)
+
+
+def scaled(value, scale):
+    """A pixel measurement at the configured scale, never smaller than 1."""
+    return max(1, int(round(value * scale)))
diff --git a/packaging/debian/postinst b/packaging/debian/postinst
index 00ae229..db8e168 100755
--- a/packaging/debian/postinst
+++ b/packaging/debian/postinst
@@ -22,6 +22,7 @@ chmod 0755 /usr/local/bin/classroom-window
 chmod 0755 /usr/local/bin/classroom-dvd
 chmod 0755 /usr/local/bin/classroom-dvd-css-setup
 chmod 0755 /usr/local/bin/classroom-notify-test
+chmod 0755 /usr/local/bin/classroom-notifications
 
 # Reading the optical drive needs group cdrom. Takes effect at the next
 # login, which the OTA reboot provides.
@@ -38,13 +39,18 @@ CHANNEL=stable
 
 # Set to true on classrooms that have a DVD drive.
 DVD_ENABLED=false
+
+# Size of the dock, clock and notifications, 0.8 to 1.5.
+# Larger rooms and larger TVs want a larger number.
+UI_SCALE=1.0
 CONFIG
 
     chmod 0644 /etc/ekklesia-classroom/device.conf
 fi
 
-# Make the DVD option discoverable on classrooms installed before it
-# existed. false is what those rooms already do, so nothing changes.
+# Make the settings discoverable on classrooms installed before they
+# existed. Both defaults are what those rooms already do, so nothing
+# about their behaviour changes.
 if ! grep -q '^DVD_ENABLED=' /etc/ekklesia-classroom/device.conf; then
     cat >> /etc/ekklesia-classroom/device.conf <<'CONFIG'
 
@@ -53,6 +59,15 @@ DVD_ENABLED=false
 CONFIG
 fi
 
+if ! grep -q '^UI_SCALE=' /etc/ekklesia-classroom/device.conf; then
+    cat >> /etc/ekklesia-classroom/device.conf <<'CONFIG'
+
+# Size of the dock, clock and notifications, 0.8 to 1.5.
+# Larger rooms and larger TVs want a larger number.
+UI_SCALE=1.0
+CONFIG
+fi
+
 systemctl daemon-reload || true
 
 systemctl enable ekklesia-classroom-update.timer || true
diff --git a/scripts/classroom-dock b/scripts/classroom-dock
index c926a0b..ed38524 100755
--- a/scripts/classroom-dock
+++ b/scripts/classroom-dock
@@ -12,53 +12,38 @@ gi.require_version("GtkLayerShell", "0.1")
 
 from gi.repository import Gtk, Gdk, GdkPixbuf, GLib, GtkLayerShell
 
+sys.path.insert(0, "/usr/local/lib/ekklesia-classroom")
+
+from classroom_config import (  # noqa: E402
+    enabled,
+    read_device_config,
+    scaled,
+    ui_scale,
+)
+
 # Optional on purpose. The dock is the one thing the classroom cannot
 # afford to lose, so a missing DVD helper simply disables disc detection
 # instead of taking the whole shell down.
-sys.path.insert(0, "/usr/local/lib/ekklesia-classroom")
-
 try:
     import classroom_optical as optical
 except ImportError:
     optical = None
 
 
-CONFIG_FILE = Path("/etc/ekklesia-classroom/device.conf")
-CSS_FILE = Path("/etc/ekklesia-classroom/dock/style.css")
+CSS_FILE = Path("/etc/ekklesia-classroom/dock/style.css.in")
 ICON_DIR = Path("/etc/ekklesia-classroom/icons")
 
 DVD_POLL_SECONDS = 2
 
+# Every measurement in the shell, at UI_SCALE=1.0. The CSS template
+# carries the same numbers; these are the ones GTK needs in Python.
+SHELL_HEIGHT = 76
+DOCK_SPACING = 10
+CLOCK_EDGE_PADDING = 20
 
-def read_device_config():
-    config = {}
-
-    if not CONFIG_FILE.exists():
-        return config
-
-    for raw_line in CONFIG_FILE.read_text().splitlines():
-        line = raw_line.strip()
-
-        if not line or line.startswith("#") or "=" not in line:
-            continue
-
-        key, value = line.split("=", 1)
-        config[key.strip()] = value.strip()
-
-    return config
-
-
-def enabled(config, key, default=False):
-    if key not in config:
-        return default
-
-    return config[key].lower() in {
-        "1",
-        "true",
-        "yes",
-        "on",
-        "enabled",
-    }
+BROWSER_ICON_SIZE = 28
+DVD_ICON_SIZE = 40
+SANCTUARY_ICON_SIZE = 38
 
 
 def launch(command):
@@ -122,6 +107,7 @@ class ClassroomShell(Gtk.Window):
         self.set_resizable(False)
 
         self.config = read_device_config()
+        self.scale = ui_scale(self.config)
 
         self.dvd_image = None
         self.disc_ready = None
@@ -148,14 +134,16 @@ class ClassroomShell(Gtk.Window):
             True,
         )
 
-        GtkLayerShell.set_exclusive_zone(self, 76)
+        shell_height = scaled(SHELL_HEIGHT, self.scale)
+
+        GtkLayerShell.set_exclusive_zone(self, shell_height)
         GtkLayerShell.set_keyboard_interactivity(
             self,
             False,
         )
 
         layout = Gtk.Overlay()
-        layout.set_size_request(-1, 76)
+        layout.set_size_request(-1, shell_height)
 
         dock = self.build_dock()
 
@@ -181,7 +169,7 @@ class ClassroomShell(Gtk.Window):
             0,
             0,
             0,
-            20,
+            scaled(CLOCK_EDGE_PADDING, self.scale),
         )
         clock_align.add(self.clock)
 
@@ -199,7 +187,7 @@ class ClassroomShell(Gtk.Window):
     def build_dock(self):
         dock = Gtk.Box(
             orientation=Gtk.Orientation.HORIZONTAL,
-            spacing=10,
+            spacing=scaled(DOCK_SPACING, self.scale),
         )
         dock.get_style_context().add_class("dock")
 
@@ -262,9 +250,11 @@ class ClassroomShell(Gtk.Window):
         return button
 
     def browser_icon(self):
+        size = scaled(BROWSER_ICON_SIZE, self.scale)
+
         image = custom_icon(
             "browser.svg",
-            28,
+            size,
         )
 
         if image is not None:
@@ -274,14 +264,16 @@ class ClassroomShell(Gtk.Window):
             "web-browser-symbolic",
             "internet-web-browser-symbolic",
         )
-        image.set_pixel_size(28)
+        image.set_pixel_size(size)
 
         return image
 
     def dvd_icon(self):
+        size = scaled(DVD_ICON_SIZE, self.scale)
+
         image = custom_icon(
             "dvd.svg",
-            40,
+            size,
         )
 
         if image is not None:
@@ -292,7 +284,7 @@ class ClassroomShell(Gtk.Window):
             "media-optical-symbolic",
             "media-optical",
         )
-        image.set_pixel_size(28)
+        image.set_pixel_size(size)
 
         return image
 
@@ -309,9 +301,11 @@ class ClassroomShell(Gtk.Window):
             else "live-off.svg"
         )
 
+        size = scaled(SANCTUARY_ICON_SIZE, self.scale)
+
         image = custom_icon(
             filename,
-            38,
+            size,
         )
 
         if image is not None:
@@ -321,7 +315,7 @@ class ClassroomShell(Gtk.Window):
             "video-display-symbolic",
             "video-display",
         )
-        image.set_pixel_size(28)
+        image.set_pixel_size(size)
 
         return image
 
@@ -364,11 +358,46 @@ class ClassroomShell(Gtk.Window):
         return True
 
 
-def load_css():
-    provider = Gtk.CssProvider()
-    provider.load_from_path(
-        str(CSS_FILE)
-    )
+def render_css(scale):
+    """Resolve the measurement tokens in the stylesheet template."""
+    css = CSS_FILE.read_text()
+
+    measurements = {
+        "dock-radius": 24,
+        "dock-padding-v": 8,
+        "dock-padding-h": 10,
+        "button-radius": 16,
+        "button-padding": 6,
+        "button-size": 44,
+        "clock-radius": 16,
+        "clock-padding-v": 7,
+        "clock-padding-h": 12,
+        "clock-font": 17,
+    }
+
+    for token, value in measurements.items():
+        css = css.replace(
+            f"@{token}@",
+            str(scaled(value, scale)),
+        )
+
+    return css
+
+
+def load_css(scale):
+    # Styling is worth losing before the dock is. A stylesheet that will
+    # not parse leaves an unstyled but working shell rather than no shell.
+    try:
+        provider = Gtk.CssProvider()
+        provider.load_from_data(
+            render_css(scale).encode("utf-8")
+        )
+    except (OSError, GLib.Error) as error:
+        print(
+            f"classroom-dock: stylesheet not applied: {error}",
+            file=sys.stderr,
+        )
+        return
 
     screen = Gdk.Screen.get_default()
 
@@ -380,7 +409,7 @@ def load_css():
 
 
 def main():
-    load_css()
+    load_css(ui_scale(read_device_config()))
 
     shell = ClassroomShell()
     shell.connect(
diff --git a/scripts/classroom-notifications b/scripts/classroom-notifications
new file mode 100755
index 0000000..97ef84c
--- /dev/null
+++ b/scripts/classroom-notifications
@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+
+"""Starts mako with the classroom styling at the room's UI scale.
+
+mako only reads ~/.config, and its measurements have to follow UI_SCALE,
+so the packaged template is resolved into the session's runtime directory
+and mako is pointed at the result.
+"""
+
+import os
+import sys
+from pathlib import Path
+
+sys.path.insert(0, "/usr/local/lib/ekklesia-classroom")
+
+from classroom_config import read_device_config, scaled, ui_scale  # noqa: E402
+
+MAKO = "/usr/bin/mako"
+TEMPLATE = Path("/etc/ekklesia-classroom/mako/config.in")
+
+# The same measurements the template carries, at UI_SCALE=1.0.
+MEASUREMENTS = {
+    "font-size": 12,
+    "radius": 18,
+    "padding-v": 14,
+    "padding-h": 18,
+    "margin": 18,
+    "width": 380,
+    "height": 160,
+    "icon-size": 48,
+}
+
+
+def runtime_directory():
+    base = os.environ.get("XDG_RUNTIME_DIR") or "/tmp"
+
+    directory = Path(base) / "ekklesia-classroom"
+    directory.mkdir(parents=True, exist_ok=True)
+
+    return directory
+
+
+def render(scale):
+    config = TEMPLATE.read_text()
+
+    for token, value in MEASUREMENTS.items():
+        config = config.replace(
+            f"@{token}@",
+            str(scaled(value, scale)),
+        )
+
+    return config
+
+
+def main():
+    scale = ui_scale(read_device_config())
+
+    try:
+        path = runtime_directory() / "mako.config"
+        path.write_text(render(scale))
+        config_argument = str(path)
+    except OSError as error:
+        # Better plain notifications than none at all.
+        print(
+            f"classroom-notifications: falling back to the unscaled template: {error}",
+            file=sys.stderr,
+        )
+        config_argument = str(TEMPLATE)
+
+    os.execv(MAKO, [MAKO, "--config", config_argument])
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tools/build-release.sh b/tools/build-release.sh
index 7f39e2a..4c231a1 100755
--- a/tools/build-release.sh
+++ b/tools/build-release.sh
@@ -113,7 +113,15 @@ install -Dm755 \
     "$ROOT/scripts/classroom-notify-test" \
     "$STAGE/usr/local/bin/classroom-notify-test"
 
-# Shared helpers imported by the dock and by classroom-dvd.
+install -Dm755 \
+    "$ROOT/scripts/classroom-notifications" \
+    "$STAGE/usr/local/bin/classroom-notifications"
+
+# Shared helpers imported by the classroom commands.
+install -Dm644 \
+    "$ROOT/lib/classroom_config.py" \
+    "$STAGE/usr/local/lib/ekklesia-classroom/classroom_config.py"
+
 install -Dm644 \
     "$ROOT/lib/classroom_optical.py" \
     "$STAGE/usr/local/lib/ekklesia-classroom/classroom_optical.py"
@@ -126,15 +134,15 @@ install -Dm755 \
     "$ROOT/scripts/classroom-dock" \
     "$STAGE/usr/local/bin/classroom-dock"
 
+# Stylesheet and notification templates. Both carry measurement tokens
+# that are resolved from UI_SCALE when the session starts.
 install -Dm644 \
-    "$ROOT/config/dock/style.css" \
-    "$STAGE/etc/ekklesia-classroom/dock/style.css"
+    "$ROOT/config/dock/style.css.in" \
+    "$STAGE/etc/ekklesia-classroom/dock/style.css.in"
 
-# Notification styling, matched to the dock. mako only searches
-# ~/.config, so sway starts it with an explicit --config path.
 install -Dm644 \
-    "$ROOT/config/mako/config" \
-    "$STAGE/etc/ekklesia-classroom/mako/config"
+    "$ROOT/config/mako/config.in" \
+    "$STAGE/etc/ekklesia-classroom/mako/config.in"
 
 # Chrome enterprise policy: suppress first-run and sign-in nags, and pin
 # Home to Wonder Ink. Nothing here restricts where teachers can browse.