Chapter 1: Common Sizes & Measurement Conventions

Created by Sarah Choi (prompt writer using ChatGPT)

Common Sizes & Measurement Conventions for Prop Concept Artists: Dimensions, Standards, and Reference

Scale is the quiet law that makes props feel real. A design can be beautifully rendered and still fail if a finger cannot fit under a latch, if a screw head is impossibly tiny, or if a hose coupling would burst at the implied pressure. This article collects practical size ranges, measurement habits, and callout conventions tailored to both concept and production artists so your props read correctly at a glance and build cleanly downstream.

A good rule: design with people, parts, and processes in mind. People suggest anthropometric bounds; parts suggest commercial standards; processes suggest walls, clearances, and fillets. When all three agree, your drawings become manufacturable stories.

1) Human Scale: Hands, Reach, and Readability

Hand grips and spans. Bare‑hand comfortable bar diameters fall around 28–35 mm for mixed users; fine‑tool handles sit at 18–25 mm; heavy grips for gloved hands are 35–45 mm. A two‑finger pinch tab wants 10–14 mm height; a three‑finger pull ring 22–30 mm internal diameter. Finger clearance under a latch or handle: minimum 18–22 mm for bare hands, 25–30 mm for light gloves, 32–38 mm for work gloves.

Buttons, switches, and knobs. Momentary push buttons that must not be fat‑fingered: 10–16 mm caps; emergency stop mushrooms: 35–45 mm. Toggle levers: 12–20 mm long with 6–9 mm ball ends. Rotary knobs for precise control: 18–28 mm diameter; for quick grabs: 30–45 mm with knurling. Detent spacing readable by feel: ~12°–18° steps.

Labels and icons (physical). Comfort‑read micro‑type on matte surfaces: 2.0–2.5 mm cap height; critical legends: 3.0–4.0 mm; distance‑read headers on equipment panels: 10–18 mm. Icon stroke weights should visually match a 0.4–0.8 mm line at 1:1.

Reach and stance. Comfortable reach on a tabletop is ~400–500 mm from body; overhead reach for 50th‑percentile users is ~2.0–2.1 m; knee‑height service panels around 450–550 mm; bench tops 860–915 mm high. Hand‑carry mass cues: one‑hand “confident lift” often implies <7 kg; two‑hand box with handles 9–18 kg.

2) Prop Size Ladders by Use Class

Pocketables (EDC, comms, scanners): 80–160 mm long, 8–24 mm thick, 80–300 g. Screens 1.2–3.0 in diagonal. Fasteners typically M2–M3 or #2–#4.

Handheld tools (drivers, cutters, welders): 160–320 mm long. Grip OD 28–40 mm. Power cables 4–8 mm OD. Battery sleds sized to cells (see below). Fasteners M3–M5 or #4–#10.

Case‑borne instruments: Pelican‑like cases 300–650 mm wide. Latch throw ~18–30 mm. Hinge knuckles 8–16 mm OD. Panel thickness 2–4 mm polymer + ribs.

Benchtop modules (chargers, analyzers): Footprint 200×200 to 400×300 mm. Display 3–7 in. Ports spaced on 12.5–25 mm centers. Rubber feet 8–15 mm high.

Floor units (generators, compressors): 700–1600 mm on longest side. Casters 75–150 mm. Panel screws M5–M8. Handles 25 mm tube OD (32–38 mm with grip).

Use ladders to keep families coherent—double sizes as capability doubles; keep handles, latches, and ports aligned to repeated modules.

3) Common Components and Their Canonical Sizes

Batteries. Cylindrical: AAA Ø10.5×44.5 mm; AA Ø14.5×50.5 mm; C Ø26.2×50 mm; D Ø34.2×61.5 mm. 18650 Ø18×65 mm; 21700 Ø21×70 mm. 9V: 26.5×17.5×48.5 mm. Pouch cells vary; common packs: 60×90×6 mm to 100×150×10 mm. Provide 0.5–1.0 mm clearance per side in sleds; spring travel 2–4 mm.

Threaded fasteners (metric). Head across‑flats (hex): M3=5.5 mm, M4=7 mm, M5=8 mm, M6=10 mm, M8=13 mm. Socket cap head OD ≈ 1.5×nominal; button head ≈ 1.7×. Common coarse pitches: M3×0.5, M4×0.7, M5×0.8, M6×1.0, M8×1.25. Clearance holes: M3=3.4, M4=4.5, M5=5.5, M6=6.6, M8=9.0 mm.

Machine screws (imperial). #4‑40 major Ø≈3 mm; #6‑32 ≈3.5 mm; #8‑32 ≈4.2 mm; #10‑24 ≈4.8 mm. Flat head countersinks usually 82° (US) or 90° (EU).

Pipe/hoses. Quick reference OD: food/air hoses 6, 8, 10, 12 mm; industrial 1/4″ (6.35), 3/8″ (9.5), 1/2″ (12.7). NPT fittings labeled by nominal ID (1/4 NPT hex flats ~14–19 mm). Garden hose GHT 3/4‑11.5 (US). Quick couplers (pneumatic) 1/4″ body ~12–14 mm spigot.

Electrical connectors. USB‑A port opening ~14×6.5 mm; USB‑C ≈ 8.4×2.6 mm; RJ45 ~14.5×8 mm; 3.5 mm TRS jack Ø 6.5 mm boss; IEC C13 inlet 21×14 mm aperture. Power rocker switches common 19×13 mm or 30×22 mm panel cutouts.

Magnets & detents. Small neodymium discs Ø6–12 mm × 2–5 mm; press‑fit pockets +0.1 mm. Detent balls Ø2–4 mm with spring travel 0.5–1.5 mm.

Displays. Seven‑segment digit height for quick read: 8–14 mm handheld; 20–38 mm benchtop. OLED/IPS modules: 0.96″ (80×160), 1.3″ (128×64), 2.4″ (320×240), 3.5″ (480×320). Bezel lips 0.8–1.5 mm; reveal gaps 0.3–0.7 mm.

4) Materials, Walls, and Clearances by Process

Injection‑molded plastics. Typical wall 2–3 mm for ABS/PC; ribs at 0.5–0.7× wall; minimum bosses Ø2× screw OD; draft 1–2°. Living hinges ~0.3–0.5 mm PP. Clip tongues 1.5–2.5 mm thick with 0.3–0.6 mm interference.

Sheet metal. Steel 1.0–3.0 mm; aluminum 1.5–4.0 mm for enclosures. Bend radius ≥ material thickness; hole to edge ≥ 1.5× thickness. PEM nuts require +1.0–1.5 mm margin.

CNC billets. Fillet internal corners to tool radius (e.g., 3 mm end mill → ≥1.6 mm fillet). Thread engagement 1–1.5× diameter in aluminum, 0.8–1.0× in steel.

3D print (FDM). Practical walls 1.2–2.0 mm; hole compensation +0.2–0.4 mm; minimum text height 1.0–1.5 mm with 0.4–0.6 mm stroke. (SLA can halve these.)

Glass and ceramics. Glass panel thicknesses 1.5–4.0 mm small; 5–8 mm large. Gaskets (silicone) 1.5–3.0 mm cord; compression 10–25%.

Provide clearances: sliding fits +0.1–0.3 mm small parts; +0.3–0.6 mm for glove‑use latches. Thermal gaps around hot parts 1–3 mm plus vent path.

5) Dimensional Conventions, Rounding, and Callouts

Units discipline. Pick metric by default unless fiction or franchise dictates imperial. If mixed, isolate domains: mechanical metric (M fasteners), legacy hoses imperial. Always annotate units in the title block and first occurrence of a dimension string.

Rounding. Use “design intent” numbers: 5, 10, 12, 15, 20, 25, 30 mm, etc. Reserve fractional mm only where necessary (press fits, wall equalization). For imperial, prefer eighths/quarters for visuals (1/8″, 1/4″, 1/2″) and decimals for callouts (0.25″).

Dimension styles. Dimension to centers and datums, not to arbitrary edges. Call hole patterns by pitch (e.g., 25 mm grid). On circular parts, use polar arrays (Ø and angle). For thickness, specify total stack and sub‑layers if the shader/prop will bake them (e.g., 1.5 mm plate + 0.2 mm paint).

GD&T lite. Keep it readable: flatness or parallelism if plates must mate; perpendicularity on bosses; runout on rotating parts. Avoid dense symbol soup in concept—convey tolerance intent verbally in notes (“flush within ±0.3 mm”).

Exploded metrics. When showing assemblies, annotate fastener spec (e.g., M4×12 SHCS), torque symbol, and sequence numbers. Use consistent arrow heads and step numbers.

Scale bars & rulers. Put a 100 mm (or 4″) scale bar on concept sheets; add a human hand silhouette at 100% for quick gut checks. Include a common object (AA cell, credit card 85.6×53.98 mm) once per page to anchor scale.

6) Camera, Texels, and On‑Screen Legibility

Texel density. Plan smallest readable label size against texels: if TD is 10.24 px/cm (a common game target ≈ 26 px/in), a 2 mm cap height needs ~0.8 px—too low; either increase TD near control clusters or move tertiary micro‑type to decals. Keep icon strokes ≥1.0–1.5 px at intended distance.

Mip and TAA survival. Avoid 1‑px lines at oblique angles; add keylines or thicken strokes. Prefer bars/rings to dots for LEDs. Align decals to UV to minimize shimmer.

Framing. For hero props, design orthos at known FOV (e.g., 35–50 mm full‑frame equivalent). Include a camera distance note so production can match perspective in engine shots.

7) Real‑World Standards to Echo (Fiction‑Friendly)

Panels and grids. 10 mm and 25 mm grids dominate many industrial interfaces; rack gear uses 19″ width with 1U = 44.45 mm height. DIN rail modules width multiples of 17.5 mm.

Pallets and crates. ISO pallets 1200×800 mm (EU) and 1200×1000; US 48×40″ (1219×1016 mm). Shipping containers: 20 ft (external ~6.06×2.44×2.59 m) and 40 ft (~12.19×2.44×2.59 m). Door clear openings ~2.34 m high.

Doors and passage. Residential doors 760–915 mm; industrial 900–1200 mm. Clearance for carts 800–1000 mm. Handrails Ø 32–45 mm.

Paper & labels. A‑series: A4 210×297 mm, A3 297×420 mm; label stickers often 10×50, 25×75, 50×100 mm. Barcode quiet zones ≥ 2.5 mm.

Safety spaces. Guard mesh apertures <12 mm to prevent finger ingress; pinch‑point warning zones 25–50 mm around hinge arcs.

Use standards as rhythm, not constraint—fictional worlds that echo these numbers feel instantly credible.

8) Reference Gathering & Calibration

Measure like a tech. Keep a 150 mm caliper, steel rule, and tape. Photograph props next to a scale card or an AA battery; keep lens at 50–70 mm equivalent to reduce distortion. Note process: “ABS, 2.5 mm wall, 1° draft.” Record screw specs from heads (e.g., hex 3 mm driver → likely M2.5/M3). Build a personal size library with sketches and numbers for common parts.

Photogrammetry sanity. If using photos to scale, include two non‑collinear scale objects. Correct perspective before tracing. Trust thickness cues: if a polymer case looks 2.5–3.0 mm at edges, it probably is.

9) Callouts that Downstream Teams Love

Write concise, ordered notes. Lead with function, then size: “Latch: 3‑finger pull, 28 mm grip depth, 30 N spring.” For fasteners: “Panel: M4×10 button heads, 6×, torque 2.5 N·m, sequence 1‑6.” For ports: “DC IN: 24 VDC, Ø5.5/2.5 mm barrel, polarity tip‑pos; label cap height 3 mm.” For assemblies: include overall dims (L×W×H), mass target, center of gravity location if relevant. Avoid burying critical dimensions in the weeds; gray out tertiary notes or move to a detail box.

Visual structure. Keep dimension arrows outside silhouettes when possible. Use consistent arrowheads and text height across sheets. Group callouts by zone and draw faint boundary boxes to reduce spaghetti lines. Add a mini‑legend for symbols used.

10) Quick Cheats (Pin to Your Monitor)

— Grip OD: 28–35 mm bare; 35–45 mm gloved. — Finger clearance under handles: ≥22 mm bare; ≥30 mm gloved. — Push button caps: 10–16 mm; E‑stop: 35–45 mm. — Small readable text: ≥2.0–2.5 mm cap height. — Injection wall: 2–3 mm ABS/PC; draft 1–2°. — Sheet metal: 1–3 mm; bend radius ≥ thickness. — Common fasteners on handhelds: M3–M5; panels: M4–M6. — Hose OD (small tools): 6–12 mm; power cord OD: 5–9 mm. — LED rings read better than 1‑px dots; add keylines. — Use 10/12.5/25 mm grids for port spacing and panel rhythm.

Designing with common sizes and measurement conventions is not about limiting creativity; it is about giving your fiction a scaffold strong enough to hold weight. When grips feel right, labels read at the right distance, fasteners fit plausible tools, and walls match their process, your props gain that rare quality: they look like they were made by someone, for someone, for a reason—and downstream teams can build them without guesswork.