Chapter 2: Scale References (Hands, Coins, Rulers)

Created by Sarah Choi (prompt writer using ChatGPT)

Scale References (Hands, Coins, Rulers) for Prop Concept Artists: Dimensions, Standards, and Practical Reference

Scale reference is the fastest way to make a prop feel real. A believable latch, a plausible screw, or a comfortable handle can all be judged in a heartbeat when your image pairs the design with a familiar object. Hands, coins, and rulers are the classic trio—ubiquitous, portable, and instantly legible. Used thoughtfully, they anchor dimensions, accelerate team decisions, and keep your work aligned with production reality. This article explains how to build a disciplined scale‑reference practice for both concept and production artists, turning casual “banana for scale” jokes into a professional system.

Begin by deciding what your audience must learn at a glance. A single reference clarifies size class; a small set of references clarifies ergonomics and manufacturing. Hands indicate human fit; coins and credit cards provide exact numbers; rulers prove measurement chain‑of‑custody. Choose the reference that best serves the page: a hand for grip logic, a coin for micro‑scale hardware, a ruler for technical sign‑off. Avoid clutter—one hero reference beats five noisy ones.

Hands are the most persuasive reference because they embody use. But hands vary. A 5th‑percentile female palm and a 95th‑percentile male palm have dramatically different spans. When you stage hand references, declare context in a caption: “Reference hand: 50th percentile, glove size M.” For general audiences, target average hands: palm breadth ~8.0–8.5 cm; index finger pad diameter ~1.6–1.8 cm; finger thickness ~16–20 mm; thumb pad ~20–25 mm wide. Show believable grasp types: pinch (index + thumb), power grip (all fingers), hook (fingers only), and lateral pinch (key grip). Keep fingers relaxed; death grips mislead scale and ergonomics. For gloved contexts, increase clearances: light gloves add 3–6 mm to finger thickness; work gloves add 6–12 mm. Photograph hands perpendicular to the camera plane to avoid foreshortening that exaggerates or shrinks features.

Coins are compact, standardized, and optics‑friendly. They provide high‑contrast micro‑detail that reveals lens distortion instantly. Use them to anchor small mechanisms, fasteners, and ports. Place coins flat on the same plane as the prop detail; tilt introduces parallax error. Rotate coins so a known diameter is edge‑on to rulers. Typical diameters used globally include: US dime 17.91 mm, US penny 19.05 mm, US nickel 21.21 mm, US quarter 24.26 mm, US half‑dollar 30.61 mm; Euro cents/coins 16.25–25.75 mm; UK 5p 18.00 mm, 10p 24.50 mm, £1 23.03 mm. Pick the coin your audience recognizes most. If you ship globally, include a caption with the diameter to remove ambiguity.

Rulers and scale cards transform a reference photo into a measurement. Prefer steel rules with etched marks; they are thinner, flatter, and produce less parallax than plastic. Stage them on the same plane as the prop feature and align the rule edge with the feature edge you are measuring. For macro shots, a millimeter rule is essential; for larger props, a 1 cm or 1/4″ graduation avoids visual noise. Laser‑printed scale cards are excellent: print at 100% on matte stock, include both metric and imperial bars (e.g., 0–100 mm, 0–4″), and add a checkerboard corner for perspective correction. Keep a “scale slate” in your kit: a credit‑card‑size plate with 100 mm bar, 4″ bar, 10×10 mm checker, a neutral grey patch, and a serial field. Place slates near the focal area, not off in the background.

Calibration begins with optics. Lens choice determines perceived scale. For small props, shoot at 50–70 mm full‑frame equivalent to minimize distortion; for large props, step back and use 70–105 mm. Keep the image plane parallel to the prop face when capturing orthographic reads; small tilts can skew dimensions by several percent. Set a longer working distance and move the camera rather than zooming if your glass breathes. Use a tripod and level; even a phone clamp with a bubble level improves repeatability. In software, correct distortion and perspective before you measure; trust your calibrated ruler or scale slate more than the raw pixel count.

On the page, show scale in multiple registers. Pair a macro inset with a global view. The global view might include a hand silhouette and a 100 mm scale bar; the macro inset can include a coin and a 10 mm rule segment near a fastener cluster. Annotate units and avoid mixing dimensions on one leader line. If you work metric, keep mechanical callouts metric consistently—even if you include an imperial ruler for audience comfort. Provide a clear legend for any icons you use (e.g., a glove icon indicates gloved clearance).

In concept renders, fake what you can’t shoot. Use a consistent set of photo‑scanned hands and scale items with true physical dimensions. Place them on a shadow‑catcher and match key light direction and intensity to your render. Keep contact shadows clean; floating references destroy credibility. For stylized work, maintain proportional accuracy even if design language bends realism. If your world uses fictional currencies, define coin diameters early in the lore bible and keep them plausible relative to our world.

Avoid common pitfalls that sabotage trust. Do not let hands hover above props; ensure knuckles compress and skin creases where contact happens. Do not let coins sit on fillets or curved surfaces when claiming precise size; place them on a flat adjacent ledge. Do not curve rulers around cylinders and then read linear values without indicating curvature. Do not place references at different depths within the frame unless you clearly label which plane is the measurement plane. Do not rely on wide‑angle lenses for dramatic composition when the goal is scale truth; exaggeration at 24–35 mm will distort handles and arcs.

Anthropometric silhouettes make excellent rapid references. Include an outline of a hand at 100% behind a grip design, a side view of a head for headset scale, or a torso bust for harness concepts. When doing this, cite percentile in the caption and keep one baseline silhouette across the project. For props meant for children or armored operators, switch silhouettes and repeat key measurements (grip OD, finger clearance) so reviewers do not assume adult bare‑hand norms.

When presenting multi‑sheet designs, standardize your scale language. Put a 100 mm bar on every sheet in the same corner. Keep a persistent caption that states “All dimensions in millimeters unless noted.” Use the same coin or card across the project to build a consistent mental model. If you jump between references (e.g., AA cells, coins, rulers), always include one repeatable anchor (the 100 mm bar) on the page.

Photogrammetry and scanning benefit from thoughtful reference. Place at least two non‑collinear scale cards in the capture volume so software can solve scale even when one is occluded. Stick cards to orthogonal faces to reduce reprojection error. For turntable captures, mount a scale ring with printed tick marks and publish its diameter. Always validate the scan by measuring a known feature post‑solve and comparing to caliper values.

In engine and UI, recreate the reference discipline. Annotate orthos with a screen‑space scale: “This preview at 50 cm, 60° FOV.” If your HUD uses diegetic rulers (e.g., e‑ink scale bars), keep their tick spacing realistic. For on‑screen inventory previews, show a ghosted hand silhouette toggle to let players gauge object size, and remember to disclose whether the hand is bare or gloved.

Culture and localization affect recognition. Coins differ by region; rulers may use centimeters or inches; A‑series paper (A4 210×297 mm) is common globally, while US Letter (8.5×11″) dominates in North America. If your audience spans regions, include two references: a coin and a credit card (85.60×53.98 mm), or a AA battery (Ø14.5×50.5 mm) which is nearly universal. Caption sizes explicitly to avoid “looks right” assumptions.

Wear and materials can be scale cues by themselves. Fine hairline scratches on anodized aluminum imply small scale; orange‑peel in paint implies thick coatings; wood grain frequency hints at object size. Use these as supplemental cues, but anchor with measurable references so texture scale does not mislead. When photographing glossy surfaces, control speculars so the ruler remains legible—polarizing filters help; matte rulers help even more.

Establish a kit and ritual to keep scale consistent. Kit: steel 150 mm and 600 mm rulers; metric tape; credit‑card slate; US quarter and local coin; AA cell; colored tape; grey card; phone clamp with level; microfiber cloth. Ritual: place slate near focal area; set lens 50–70 mm eq.; level camera; align plane; take a proof shot; adjust; capture macro with coin; capture hand pose; log file names with suffixes “_scale,” “_coin,” “_hand.” Small habits avoid re‑shoots.

Deliverables that downstream teams love include a consistent scale module on every page: a 100 mm bar, coin callout with diameter, hand silhouette with percentile and glove note, and a brief line stating camera FOV and distance for orthos. Add a mini index of reference items used across the project so reviewers know what sizes to expect. On hero props, include a page that shows five views of the same reference (hand, coin, ruler, AA cell, credit card) so marketing, modeling, and fabrication all see the same truth.

Scale references are not decoration; they are contract language. When hands compress, coins sit flat, and rulers line up, you signal that dimensions matter. That signal saves time, reduces revisions, and makes your props feel like they were built by someone for someone. In concept, it buys trust; in production, it buys accuracy. Use the trio—hands, coins, rulers—deliberately, and your worlds will hold still long enough to believe.