Convert Span to Millimeter
Convert spans to millimeters instantly. 1 span = 228.6 millimeter — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Millimeter to Span converter for the reverse conversion.
Units explained
Span
A span is an Imperial unit of length equal to 9 inches (228.6 mm). Historically, it represented the distance from the tip of an extended thumb to the tip of an extended little finger.
The span derives from this natural body-measurement and was standardised at 9 inches in English customary practice.
Spans are rare in modern commerce but appear in historical English literature, biblical translation studies, and reproduction crafts. Some construction and gardening still use 'span' informally.
Ancient body-measure origin; standardised in English customary practice at 9 inches; became exact via the 1959 International Yard and Pound Agreement.
Millimeter
A millimeter is a metric unit of length equal to one thousandth of a meter (1/1000 m). It is the standard small-scale unit in the SI system and is widely used wherever sub-centimeter precision matters.
The millimeter was defined alongside the meter when France adopted the metric system in 1795, using the standard SI prefix milli- (from Latin mille, "thousand") to denote one-thousandth.
Millimeters are used in engineering drawings, machining, manufacturing, paper sizes, rainfall measurement, and any context where dimensions below one centimeter need to be specified clearly. Most rulers worldwide are marked in millimeters.
Adopted in 1795 in France as part of the original metric system; standardized internationally by the Metre Convention in 1875 and confirmed in the SI in 1960.
Span to Millimeter conversion formula
The relationship between spans and millimeters:
To convert spans to millimeters, multiply the value in spans by 228.6. To reverse, multiply millimeters by 0.0043744532.
How to use this converter
Type a value into the calculator. The result in millimeters updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Millimeter to Span converter for the reverse direction.
Step-by-step: convert spans to millimeters
- Write down the value in spans (span).
- Multiply that value by the factor 228.6.
- The product is the equivalent value in millimeters (mm).
- To reverse, multiply the millimeter value by 0.0043744532.
Worked examples
Example 1 — Convert 1 span to mm:
1 × 228.6 = 228.6 mm
Example 2 — Convert 100 span to mm:
100 × 228.6 = 22860 mm
Real-world example — Fabric and tailoring
One span of fabric converts to a value in millimeters commonly used for seam allowances. Garment patterns frequently switch between the two units on a single instruction sheet.
1 span × 228.6 = 228.6 mm
Real-world example — Body height conversion (reverse direction)
You measure 1.75 spans tall and need to fill in a gym membership form or medical record that asks for height in millimeters. This is the most-used everyday length conversion in metric-using countries.
1.75 span × 228.6 = 400.05 mm
Real-world example — Pet and accessory dimensions
A 3-span dog leash equals a tidy round value in millimeters. Pet-supply shopping frequently mixes the two units across product specifications.
3 span × 228.6 = 685.8 mm
Span to Millimeter conversion table
Standard reference values for converting spans to millimeters:
| Span [span] | Millimeter [mm] |
|---|---|
| 0.01 | 2.286 |
| 0.1 | 22.86 |
| 1 | 228.6 |
| 2 | 457.2 |
| 3 | 685.8 |
| 4 | 914.4 |
| 5 | 1143 |
| 10 | 2286 |
| 20 | 4572 |
| 30 | 6858 |
| 40 | 9144 |
| 50 | 11430 |
| 100 | 22860 |
| 500 | 114300 |
| 1000 | 228600 |
Frequently asked questions
How many millimeters is 1 span?
How do I convert spans to millimeters?
How do I convert millimeters back to spans?
How many millimeters is 100 spans?
Popular length unit conversions
Convert Span to other length units
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Metric / SI (4 units)
Imperial / US Customary (26 units)
Sources & references
Conversion factor (1 span = 228.6 mm) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Hydrographic Organization — Resolution on the Nautical Mile
International authority that standardised the nautical mile at exactly 1852 m in 1929 — the value adopted worldwide for sea and air navigation.