True Size Gauge

AWG wires, standard drill bits, and nails or screws drawn at actual physical size: ASTM B258 computed conductor diameters, the ANSI/ASME B94.11M drill tables, and the published nail and screw series, rendered through a credit-card screen calibration with the calibration state always shown.

ASTM B258 · ISO/IEC 7810 · ANSI/ASME B94.11M · ASME B18.6.1

Not calibrated — assuming the CSS default of 96 px per inch; sizes are approximate. Calibrate with a credit card for true size.

Items

12 AWG

Solid conductor diameter per ASTM B258; stranded builds run slightly larger (see the AWG wire chart).

At physical size

Rendered at the uncalibrated CSS default (96 px per inch) — calibrate above for true size. Print, page zoom, and OS display scaling all change on-screen size.

12 AWG0.0808 in · 2.053 mm

About True Size Gauge — Wire, Drill Bit & Fastener Sizes at Actual Scale

The true size gauge draws wire gauges, drill bits, and fasteners at their real physical dimensions on your screen. Pick a category — AWG wires, standard drills, or nails and screws — add up to three sizes, and see them side by side at actual scale: a 12 AWG conductor next to a 4/0 feeder, a #7 number drill next to an 8.5 mm metric drill, or a 16d common nail at its full 3-1/2 inch length.

Physical size on a screen requires knowing your display's true pixel density. Browsers assume the CSS reference pixel — exactly 96 pixels per inch — which is only approximately true on most monitors and laptops. The tool therefore shows its calibration state at all times: hold any payment card (the ISO/IEC 7810 ID-1 format, 85.60 × 53.98 mm, the size of every credit and debit card) against the on-screen outline, match the outline to the card, and the tool computes your screen's real pixels-per-millimetre and remembers it on this device. Until you calibrate, sizes are approximate and the banner says so.

Wire diameters are never transcribed from a chart: they are computed live from the ASTM B258 geometric-progression formula that defines the American Wire Gauge, with the 1/0 through 4/0 aught sizes handled as gauge numbers 0 through −3. Drill diameters reuse the same ANSI/ASME B94.11M size tables as the tap drill calculator, and nail and screw dimensions come from the published fastener-size series behind the nail & screw reference chart.

How It Works

  1. Calibrate the screen (recommended): open the calibration panel, hold a real payment card flat against the outline, and drag the slider until the outline matches the card's edges exactly, then save. The calibration — your screen's true pixels per millimetre — persists on this device only and is never part of a shared link.
  2. Pick a category tab: Wires (AWG) for solid-conductor diameters computed per ASTM B258, Drill bits for the combined metric / fractional / number / letter tables, or Nails & screws for penny-size nails and wood-screw gauges.
  3. Add up to three items from the size picker. Each renders at physical scale: wires and drills as filled circles of their diameter, nails as a side profile with true shank diameter and length (the head is a stylized glyph), screws head-on at their ASME B18.6.1 major diameter.
  4. Read the labels under each item for the exact decimal dimensions in inches and millimetres, and share the comparison — the link carries the category and items, but never your device calibration.

Worked Example

How big is 12 AWG wire, really? The ASTM B258 formula gives d = 0.005 × 92^((36−12)/39) = 0.0808 in = 2.053 mm for the solid conductor. On a screen calibrated to 3.90 px/mm, the tool draws that conductor as a circle 2.053 × 3.90 ≈ 8.0 pixels across — the true physical size of the copper. Add 4/0 AWG (0.4600 in = 11.68 mm, the formula's exact anchor at n = −3) beside it and the feeder conductor renders at 45.6 px, 5.7 times the diameter of the branch-circuit wire.

Formulas

AWG solid-wire diameter (ASTM B258)
d(in) = 0.005 × 92^((36 − n) / 39)
Physical rendering
px = mm × pxPerMm
Calibration from the card match
pxPerMm = cardWidthPx ÷ 85.60

Standards & References

  • ASTM B258 — standard nominal diameters of AWG solid round wires; the d = 0.005 × 92^((36−n)/39) formula and its exact anchors at 36 AWG and 4/0
  • ISO/IEC 7810 — identification card physical characteristics; the ID-1 format (85.60 × 53.98 mm) used for screen calibration
  • ANSI/ASME B94.11M — twist drill standard behind the metric, fractional, number (#80–#1) and letter (A–Z) drill tables (shared with the tap drill calculator)
  • ASME B18.6.1 — wood screw gauge formula D = 0.060 + 0.013 × gauge for screw major diameters
  • W3C CSS Values and Units — the CSS reference pixel (1 in = 96 px) that defines the uncalibrated fallback assumption

Frequently Asked Questions

Why do I need to calibrate with a credit card?

Browsers lay pages out against the CSS reference pixel — exactly 96 pixels per inch — but almost no physical display is exactly 96 dpi at its current OS scale factor, so "1 inch" of CSS is rarely 1 physical inch. Matching the on-screen outline to a real ISO/IEC 7810 ID-1 card (85.60 mm wide — every credit, debit, and bank card) measures your screen's true pixels per millimetre. Until you do, the tool renders at the CSS assumption and the always-visible banner tells you sizes are approximate.

Does zooming the page or printing keep things at true size?

No. Browser zoom, pinch zoom, OS display scaling, and printing all change the physical size of a CSS pixel, which breaks the calibration. Calibrate at 100% zoom and keep it there while comparing sizes; recalibrate if you change monitors or display scaling. Printed output follows the printer's own scaling, not the screen calibration, so this tool makes no true-size claim on paper.

Is the wire circle the cable I would buy at the store?

It is the bare solid conductor diameter per ASTM B258 — no insulation. Building wire is also commonly stranded, and a stranded build of the same gauge runs slightly larger in overall diameter than the solid equivalent (NEC Chapter 9 Table 8 lists stranded dimensions). Insulated cable adds the insulation wall on top of that. Use the AWG ampacity chart for stranded overall diameters.

Why don't screws show a length?

Wood screws are sold by gauge (diameter) and length independently — a #8 screw exists in dozens of lengths — and the verified dataset behind the nail & screw chart publishes the gauge formula, not a length series. So screws render head-on as a circle at their ASME B18.6.1 major diameter (D = 0.060 + 0.013 × gauge). Nails do carry a defined length per penny size, so they render in full side profile with true length and shank diameter.

Is my calibration shared when I share a link?

No — deliberately. The shared URL carries only the category and the compared items. Pixels-per-millimetre is a property of your specific screen; importing it onto someone else's display would render everything at the wrong size. The calibration lives only in your browser's local storage on this device, and the recipient's own calibration (or the default assumption) applies on their end.