diff --git a/frontend/src/views/Print.vue b/frontend/src/views/Print.vue
index e2ac7f5..dfdd84b 100644
--- a/frontend/src/views/Print.vue
+++ b/frontend/src/views/Print.vue
@@ -95,8 +95,33 @@
                                     Connect a printer to preview and print a label.
                                 </p>
                                 <template v-else>
-                                    <div class="label-preview mb-3" v-show="selectedContent">
-                                        <canvas ref="labelCanvas"></canvas>
+                                    <div class="preview-row mb-3" v-show="selectedContent">
+                                        <div class="ruler-v">
+                                            <div class="ruler-v-corner"></div>
+                                            <div class="ruler ruler-v-ticks"
+                                                 :style="{height: (tape.printAreaPx * zoom) + 'px'}">
+                                                <span v-for="t in verticalRulerTicks" :key="'tick-' + t.mm"
+                                                      class="tick" :class="{'tick-major': t.major}"
+                                                      :style="{top: t.pos + 'px'}"></span>
+                                                <span v-for="t in verticalRulerTicks.filter(t => t.major)"
+                                                      :key="'label-' + t.mm" class="tick-label"
+                                                      :style="{top: t.pos + 'px'}">{{ t.mm }}</span>
+                                            </div>
+                                        </div>
+                                        <div class="preview-scroll">
+                                            <div class="ruler ruler-h"
+                                                 :style="{width: (printedWidthPx * zoom) + 'px'}">
+                                                <span v-for="t in horizontalRulerTicks" :key="'tick-' + t.mm"
+                                                      class="tick" :class="{'tick-major': t.major}"
+                                                      :style="{left: t.pos + 'px'}"></span>
+                                                <span v-for="t in horizontalRulerTicks.filter(t => t.major)"
+                                                      :key="'label-' + t.mm" class="tick-label"
+                                                      :style="{left: t.pos + 'px'}">{{ t.mm }}</span>
+                                            </div>
+                                            <div class="label-preview">
+                                                <canvas ref="labelCanvas"></canvas>
+                                            </div>
+                                        </div>
                                     </div>
 
                                     <div class="row g-2 align-items-end">
@@ -181,6 +206,9 @@ import {LABEL_TEMPLATES, BASE_VARS, DERIVED_VARS, withDerivedVars, templateConte
 const BLOB_URL = "/vendor/libweblabel.js";
 
 const MAX_ZOOM = 4;			/* never magnify the preview more than this */
+const MAX_PREVIEW_HEIGHT_PX = 300;	/* never let the on-screen preview grow taller than this */
+const RULER_TICK_MM = 1;		/* finest tick spacing the mm ruler draws */
+const RULER_MAJOR_EVERY_MM = 5;	/* every Nth tick is taller and labeled with its mm value */
 
 export default {
     name: "Print",
@@ -210,6 +238,12 @@ export default {
             connected: null,
             tape: null,
             labelBitmap: null,
+            // The tape-fed preview's current on-screen scale and printed pixel width (see
+            // fitZoom/redraw) - tracked reactively, rather than read straight off the canvas
+            // element, purely so the mm ruler below can recompute its tick positions whenever
+            // either one changes.
+            zoom: 1,
+            printedWidthPx: 0,
 
             // One input per *base* template variable (see label-layouts.js's BASE_VARS) - the
             // derived ones (itemUrl, itemHandle) are format strings calculated from these, not
@@ -286,6 +320,25 @@ export default {
         canPrint() {
             return Boolean(this.tape && this.labelBitmap && !this.busy);
         },
+        // On-screen pixels per real millimeter of tape, at the preview's current zoom - what
+        // turns a physical mm into a tick position the ruler can actually draw. Only meaningful
+        // for the tape-fed preview (see redraw's printedWidthPx) - the no-webusb fallback preview
+        // isn't fed from any particular real tape/dpi, so it gets no ruler (see the template).
+        tapePxPerMm() {
+            return this.tape ? (this.tape.dpi / 25.4) * this.zoom : 0;
+        },
+        // Ticks along the tape's length (the printed bitmap's actual width, lead/trailing feed
+        // margin included, since that's real physical tape too).
+        horizontalRulerTicks() {
+            if (!this.tape || !this.printedWidthPx) {
+                return [];
+            }
+            return this.rulerTicks(this.printedWidthPx / (this.tape.dpi / 25.4));
+        },
+        // Ticks across the tape's fixed physical width.
+        verticalRulerTicks() {
+            return this.tape ? this.rulerTicks(this.tape.mediaWidthMm) : [];
+        },
     },
     watch: {
         varValues: {
@@ -324,6 +377,16 @@ export default {
             return v.replace(/([a-z])([A-Z])/g, "$1 $2").replace(/^./, c => c.toUpperCase());
         },
 
+        // One tick per RULER_TICK_MM from 0 up to totalMm, each positioned in on-screen pixels
+        // via tapePxPerMm - shared by the horizontal/vertical ruler computeds above.
+        rulerTicks(totalMm) {
+            const ticks = [];
+            for (let mm = 0; mm <= totalMm; mm += RULER_TICK_MM) {
+                ticks.push({mm, pos: mm * this.tapePxPerMm, major: mm % RULER_MAJOR_EVERY_MM === 0});
+            }
+            return ticks;
+        },
+
         async guard(fn) {
             this.error = null;
             this.busy = true;
@@ -410,7 +473,8 @@ export default {
             const bitmap = canvasToBitmap(canvas);
             bitmapToCanvas(canvas, bitmap);
             this.labelBitmap = bitmap;
-            this.fitZoom(canvas);
+            this.printedWidthPx = canvas.width;
+            this.zoom = this.fitZoom(canvas);
         },
 
         redrawFallback() {
@@ -448,16 +512,20 @@ export default {
 
         /* Fit the preview to its card without ever needing a horizontal
            scrollbar for a label this small, magnifying short labels up to
-           MAX_ZOOM rather than showing them at native (tiny) size. */
+           MAX_ZOOM rather than showing them at native (tiny) size - and never
+           past MAX_PREVIEW_HEIGHT_PX tall, however long/wide the label itself
+           runs. Returns the zoom actually used, so callers that care (see
+           redraw's ruler bookkeeping) don't have to re-derive it. */
         fitZoom(canvas) {
             const available = canvas.parentElement.clientWidth;
             if (!(available > 0)) {
-                return;
+                return 1;
             }
-            const zoom = Math.min(MAX_ZOOM, available / canvas.width);
+            const zoom = Math.min(MAX_ZOOM, available / canvas.width, MAX_PREVIEW_HEIGHT_PX / canvas.height);
             canvas.style.width = `${canvas.width * zoom}px`;
             canvas.style.height = `${canvas.height * zoom}px`;
             canvas.style.imageRendering = zoom >= 1 ? "pixelated" : "auto";
+            return zoom;
         },
 
         print() {
@@ -476,7 +544,7 @@ export default {
                 for (const entry of entries) {
                     const canvas = entry.target.querySelector("canvas");
                     if (canvas) {
-                        this.fitZoom(canvas);
+                        this.zoom = this.fitZoom(canvas);
                     }
                 }
             }, 100);
@@ -528,6 +596,7 @@ export default {
     background: rgba(127, 127, 127, .08);
     border-radius: .35rem;
     text-align: center;
+    max-height: 300px;
 }
 
 .label-preview canvas {
@@ -536,6 +605,103 @@ export default {
     box-shadow: 0 0 0 1px rgba(127, 127, 127, .5);
 }
 
+/* The tape-fed preview's mm ruler (see Print.vue's template/script) - a horizontal track above
+   the canvas and a vertical one to its left, both ticked in real physical millimeters rather than
+   preview pixels, since what they're measuring is the actual label. */
+.preview-row {
+    display: flex;
+    align-items: flex-start;
+}
+
+/* The single horizontal scroll region for a label wider than its card - the horizontal ruler and
+   the canvas are both direct children of this, so they scroll in lockstep with no JS needed to
+   keep them in sync. */
+.preview-scroll {
+    flex: 1 1 auto;
+    min-width: 0;
+    overflow-x: auto;
+}
+
+/* Overrides the standalone rule above: nested here, .label-preview must neither clip nor center
+   its canvas - overflow-x:visible lets the canvas's true width "bubble up" to .preview-scroll's
+   own scrollbar instead of scrolling twice, and text-align:left keeps the canvas flush with the
+   ruler's zero tick instead of drifting to the middle of whatever spare width this card has. */
+.preview-scroll .label-preview {
+    overflow-x: visible;
+    text-align: left;
+}
+
+.ruler-v {
+    flex: none;
+    width: 2.2rem;
+    color: rgba(127, 127, 127, .9);
+}
+
+/* Matches .ruler-h's own height below - the vertical ruler's ticks start only after this, so tick
+   0 lines up with the canvas's top edge rather than the horizontal ruler sitting above it. */
+.ruler-v-corner {
+    height: 1.6rem;
+}
+
+.ruler-v-ticks {
+    position: relative;
+    margin-top: .75rem;	/* .label-preview's own padding, so tick 0 meets the canvas, not its box */
+}
+
+.ruler-h {
+    position: relative;
+    height: 1.6rem;
+    margin-left: .75rem;	/* .label-preview's own padding, so tick 0 meets the canvas, not its box */
+    color: rgba(127, 127, 127, .9);
+}
+
+.ruler .tick {
+    position: absolute;
+    background: currentColor;
+}
+
+/* Ticks anchor to the edge nearest the canvas (right for the vertical ruler, bottom for the
+   horizontal one) and grow outward from it, so they read as pointing at the label; the mm labels
+   sit on the opposite, outer edge, out of the ticks' way. */
+.ruler-v-ticks .tick {
+    right: 0;
+    width: .4rem;
+    height: 1px;
+}
+
+.ruler-v-ticks .tick-major {
+    width: .7rem;
+}
+
+.ruler-h .tick {
+    bottom: 0;
+    width: 1px;
+    height: .4rem;
+}
+
+.ruler-h .tick-major {
+    height: .7rem;
+}
+
+.tick-label {
+    position: absolute;
+    font-size: .6rem;
+    line-height: 1;
+    white-space: nowrap;
+}
+
+/* transform, not a fixed em nudge, so the label's actual center - not its edge - lands on the
+   tick's mm position (t.pos, set inline), whatever the text's width/height happens to be. */
+.ruler-v-ticks .tick-label {
+    left: 0;
+    transform: translateY(-50%);
+}
+
+.ruler-h .tick-label {
+    top: 0;
+    transform: translateX(-50%);
+}
+
 .copies-input {
     width: 5.5rem;
 }