{"id":495,"date":"2026-09-20T08:38:33","date_gmt":"2026-09-20T08:38:33","guid":{"rendered":"https:\/\/envelopedock.com\/uncategorized\/envelope-size-conversion\/"},"modified":"2026-09-20T08:38:33","modified_gmt":"2026-09-20T08:38:33","slug":"envelope-size-conversion","status":"publish","type":"post","link":"https:\/\/envelopedock.com\/es\/resources\/design-standards\/envelope-size-conversion\/","title":{"rendered":"Envelope Size Conversion: mm to Inches Chart for Every Standard"},"content":{"rendered":"

Introducci\u00f3n<\/h2>\n\n

Envelope sizes are quoted in two unit systems, and neither one converts cleanly to the other. US commercial sizes were designed in inches, ISO sizes were designed in millimetres, and a conversion that looks trivial \u2014 one inch equals 25.4 millimetres \u2014 produces answers with long decimals that have to be rounded before they are useful.<\/p>\n\n

That rounding is where ordering mistakes begin. A size quoted as 4.33 inches is really 110 millimetres, and treating the rounded figure as exact is how buyers end up with an envelope that does not quite fit.<\/p>\n\n

This guide gives the conversion formula, the rounding convention, and a full conversion table covering the US commercial sizes and the ISO C, B, and A series in both units.<\/p>\n\n

Why Conversions Cause Problems<\/h2>\n\n

Three properties of envelope sizing make conversion harder than it looks.<\/p>\n\n\n
Propiedad<\/th>Consecuencia<\/th><\/tr>\n
Two design origins<\/strong><\/td>US sizes are inch-native, ISO sizes are mm-native<\/td><\/tr>\n
Non-terminating decimals<\/strong><\/td>110 mm is 4.3307\u2026 inches, not 4.33 exactly<\/td><\/tr>\n
Rounded catalogue figures<\/strong><\/td>Published inches are already approximations<\/td><\/tr>\n<\/table>\n\n

The practical result is that a converted figure should be treated as a description, not a specification.<\/p>\n\n\n
If you order by\u2026<\/th>Uso<\/th><\/tr>\n
Inches<\/strong><\/td>US commercial sizes (#10, #9, 6\u00d79)<\/td><\/tr>\n
Millimetres<\/strong><\/td>ISO sizes (DL, C4, C5, C6, B5)<\/td><\/tr>\n
A converted figure<\/strong><\/td>Confirm the original unit before ordering<\/td><\/tr>\n<\/table>\n\n

The Conversion Formula<\/h2>\n\n

The conversion is a single multiplication or division.<\/p>\n\n\n
Direcci\u00f3n<\/th>Formula<\/th><\/tr>\n
Inches to millimetres<\/strong><\/td>mm = inches \u00d7 25.4<\/td><\/tr>\n
Millimetres to inches<\/strong><\/td>inches = mm \u00f7 25.4<\/td><\/tr>\n<\/table>\n\n

Worked examples:<\/p>\n\n\n
Original<\/th>Calculation<\/th>Resultado<\/th><\/tr>\n
#10 width: 4\u215b in<\/strong><\/td>4.125 \u00d7 25.4<\/td>104.8 mm<\/td><\/tr>\n
#10 length: 9\u00bd in<\/strong><\/td>9.5 \u00d7 25.4<\/td>241.3 mm<\/td><\/tr>\n
DL width: 110 mm<\/strong><\/td>110 \u00f7 25.4<\/td>4.33 in<\/td><\/tr>\n
DL length: 220 mm<\/strong><\/td>220 \u00f7 25.4<\/td>8.66 in<\/td><\/tr>\n<\/table>\n\n

The US figures convert to short decimals and then to round millimetres; the ISO figures convert to long decimals that round to two places.<\/p>\n\n

Rounding Conventions<\/h2>\n\n

Published conversions vary in how many decimal places they carry.<\/p>\n\n\n
Precision<\/th>Example (110 mm)<\/th>Uso t\u00edpico<\/th><\/tr>\n
Exact<\/strong><\/td>4.3307086 in<\/td>Engineering, never catalogue<\/td><\/tr>\n
Two decimals<\/strong><\/td>4.33 in<\/td>Catalogue listing<\/td><\/tr>\n
One decimal<\/strong><\/td>4.3 in<\/td>Rough comparison<\/td><\/tr>\n
Fractional<\/strong><\/td>4 5\/16 in<\/td>North American stationery<\/td><\/tr>\n<\/table>\n\n

For ordering, the safe rule is to specify in the unit the envelope was designed in:<\/p>\n\n\n
Sobre<\/th>Design Unit<\/th>Specify In<\/th><\/tr>\n
#10, #9, #6\u00be<\/strong><\/td>Inches<\/td>Inches<\/td><\/tr>\n
DL, C-series, B-series<\/strong><\/td>Millimetres<\/td>Millimetres<\/td><\/tr>\n<\/table>\n\n

US Commercial Sizes<\/h2>\n\n

These sizes are inch-native; the millimetre figures are conversions.<\/p>\n\n\n
Tama\u00f1o<\/th>Inches<\/th>Millimetres<\/th><\/tr>\n
#6\u00be<\/strong><\/td>3\u215d \u00d7 6\u00bd in<\/td>92.1 \u00d7 165.1 mm<\/td><\/tr>\n
#7\u00be (Monarch)<\/strong><\/td>3\u215e \u00d7 7\u00bd pulg.<\/td>98.4 \u00d7 190.5 mm<\/td><\/tr>\n
#9<\/strong><\/td>3\u215e \u00d7 8\u215e in<\/td>98.4 \u00d7 225.4 mm<\/td><\/tr>\n
#10<\/strong><\/td>4\u215b \u00d7 9\u00bd pulg<\/td>104.8 \u00d7 241.3 mm<\/td><\/tr>\n
6\u00d79<\/strong><\/td>6 \u00d7 9 in<\/td>152.4 \u00d7 228.6 mm<\/td><\/tr>\n
9\u00d712<\/strong><\/td>9 \u00d7 12 in<\/td>228.6 \u00d7 304.8 mm<\/td><\/tr>\n
10\u00d713<\/strong><\/td>10 \u00d7 13 in<\/td>254 \u00d7 330.2 mm<\/td><\/tr>\n<\/table>\n\n

Note that the US sizes convert to millimetre values with one decimal, not to round numbers \u2014 a #10 is 104.8 mm wide, not 105 mm.<\/p>\n\n

ISO C-Series Sizes<\/h2>\n\n

These are millimetre-native; the inch figures are conversions.<\/p>\n\n\n
Tama\u00f1o<\/th>Millimetres<\/th>Inches<\/th><\/tr>\n
C6<\/strong><\/td>114 \u00d7 162 mm<\/td>4.49 \u00d7 6.38 in<\/td><\/tr>\n
C5<\/strong><\/td>162 \u00d7 229 mm<\/td>6.38 \u00d7 9.02 in<\/td><\/tr>\n
C4<\/strong><\/td>229 \u00d7 324 mm<\/td>9.02 \u00d7 12.76 in<\/td><\/tr>\n<\/table>\n\n\n
Tama\u00f1o<\/th>Contiene<\/th>Detail Page<\/th><\/tr>\n
C6<\/strong><\/td>A4 doblado en cuatro partes<\/td>\u2014<\/td><\/tr>\n
C5<\/strong><\/td>A4 doblado por la mitad<\/td>Tama\u00f1o de sobre C5<\/a><\/td><\/tr>\n
C4<\/strong><\/td>A4 plano<\/td>C4 envelope size<\/a><\/td><\/tr>\n<\/table>\n\n

ISO B-Series Sizes<\/h2>\n\n

The B-series sits between A sizes, and these are millimetre-native.<\/p>\n\n\n
Tama\u00f1o<\/th>Millimetres<\/th>Inches<\/th><\/tr>\n
B6<\/strong><\/td>125 \u00d7 176 mm<\/td>4.92 \u00d7 6.93 in<\/td><\/tr>\n
B5<\/strong><\/td>176 \u00d7 250 mm<\/td>6.93 \u00d7 9.84 in<\/td><\/tr>\n
B4<\/strong><\/td>250 \u00d7 353 mm<\/td>9.84 \u00d7 13.90 in<\/td><\/tr>\n<\/table>\n\n

ISO A-Series Reference<\/h2>\n\n

The A-series defines the paper, not the envelope, but the figures are needed when checking whether contents will fit.<\/p>\n\n\n
Tama\u00f1o<\/th>Millimetres<\/th>Inches<\/th>Fits Envelope<\/th><\/tr>\n
A6<\/strong><\/td>105 \u00d7 148 mm<\/td>4.13 \u00d7 5.83 in<\/td>C6<\/td><\/tr>\n
A5<\/strong><\/td>148 \u00d7 210 mm<\/td>5.83 \u00d7 8.27 in<\/td>C5<\/td><\/tr>\n
A4<\/strong><\/td>210 \u00d7 297 mm<\/td>8.27 \u00d7 11.69 in<\/td>C4<\/td><\/tr>\n<\/table>\n\n

The DL format is the exception: it is sized to hold an A4 sheet folded in thirds rather than to hold a whole A size. For its dimensions, see the tama\u00f1o de sobre DL<\/a> .<\/p>\n\n\n
Formato<\/th>Millimetres<\/th>Inches<\/th><\/tr>\n
DL<\/strong><\/td>110 \u00d7 220 mm<\/td>4.33 \u00d7 8.66 in<\/td><\/tr>\n<\/table>\n\n

Master Conversion Table<\/h2>\n\n

The full list in one place, sorted by approximate size.<\/p>\n\n\n
Sobre<\/th>Millimetres<\/th>Inches<\/th>Serie<\/th><\/tr>\n
#6\u00be<\/strong><\/td>92.1 \u00d7 165.1<\/td>3\u215d \u00d7 6\u00bd<\/td>EE. UU.<\/td><\/tr>\n
#7\u00be Monarch<\/strong><\/td>98.4 \u00d7 190.5<\/td>3\u215e \u00d7 7\u00bd<\/td>EE. UU.<\/td><\/tr>\n
#9<\/strong><\/td>98.4 \u00d7 225.4<\/td>3\u215e \u00d7 8\u215e<\/td>EE. UU.<\/td><\/tr>\n
#10<\/strong><\/td>104.8 \u00d7 241.3<\/td>4\u215b \u00d7 9\u00bd<\/td>EE. UU.<\/td><\/tr>\n
DL<\/strong><\/td>110 \u00d7 220<\/td>4.33 \u00d7 8.66<\/td>ISO<\/td><\/tr>\n
C6<\/strong><\/td>114 \u00d7 162<\/td>4.49 \u00d7 6.38<\/td>ISO<\/td><\/tr>\n
B6<\/strong><\/td>125 \u00d7 176<\/td>4.92 \u00d7 6.93<\/td>ISO<\/td><\/tr>\n
6\u00d79<\/strong><\/td>152.4 \u00d7 228.6<\/td>6 \u00d7 9<\/td>EE. UU.<\/td><\/tr>\n
C5<\/strong><\/td>162 \u00d7 229<\/td>6.38 \u00d7 9.02<\/td>ISO<\/td><\/tr>\n
B5<\/strong><\/td>176 \u00d7 250<\/td>6.93 \u00d7 9.84<\/td>ISO<\/td><\/tr>\n
C4<\/strong><\/td>229 \u00d7 324<\/td>9.02 \u00d7 12.76<\/td>ISO<\/td><\/tr>\n
9\u00d712<\/strong><\/td>228.6 \u00d7 304.8<\/td>9 \u00d7 12<\/td>EE. UU.<\/td><\/tr>\n
B4<\/strong><\/td>250 \u00d7 353<\/td>9.84 \u00d7 13.90<\/td>ISO<\/td><\/tr>\n
10\u00d713<\/strong><\/td>254 \u00d7 330.2<\/td>10 \u00d7 13<\/td>EE. UU.<\/td><\/tr>\n<\/table>\n\n

For the complete size index, see our tama\u00f1os de sobre<\/a> centro.<\/p>\n\n

Three Ways Buyers Get the Size Wrong<\/h2>\n\n

Conversion errors tend to fall into three patterns.<\/p>\n\n

1. Confusing the envelope’s outer size with its inner capacity.<\/strong>
An envelope listed at 110 \u00d7 220 mm is the outer dimension. The usable interior is smaller, and a 110 \u00d7 220 mm card will not fit inside it.<\/p>\n\n\n
Medida<\/th>What It Describes<\/th><\/tr>\n
Outer size<\/strong><\/td>The finished envelope<\/td><\/tr>\n
Inner capacity<\/strong><\/td>What actually fits<\/td><\/tr>\n
Insert clearance<\/strong><\/td>The margin left for the contents<\/td><\/tr>\n<\/table>\n\n

2. Treating a rounded conversion as exact.<\/strong>
4.33 inches and 110 millimetres differ by about a twentieth of a millimetre, which is harmless on its own \u2014 but a size rounded down by a full millimetre can be the difference between a card that slides in and one that catches.<\/p>\n\n\n
Riesgo<\/th>Efecto<\/th><\/tr>\n
Rounding down<\/strong><\/td>Contents too tight<\/td><\/tr>\n
Rounding up<\/strong><\/td>Contents loose, may shift<\/td><\/tr>\n
Mixing units in one spec<\/strong><\/td>Layout and tooling mismatch<\/td><\/tr>\n<\/table>\n\n

3. Forgetting that postage class is judged on dimensions, not on the name.<\/strong>
A “6\u00d79 envelope” and a “C5 envelope” are close in size, but postal class depends on actual measured dimensions and thickness, not on what the format is called.<\/p>\n\n\n
Verificar<\/th>Por qu\u00e9<\/th><\/tr>\n
Measure the finished envelope<\/strong><\/td>Class follows measurements<\/td><\/tr>\n
Mida el grosor con el contenido<\/strong><\/td>Thickness can change the class<\/td><\/tr>\n
Confirm current local limits<\/strong><\/td>Thresholds are not universal<\/td><\/tr>\n<\/table>\n\n

Conclusi\u00f3n<\/h2>\n\n

Envelope size conversion<\/strong> is a single formula \u2014 inches \u00d7 25.4 for millimetres, or millimetres \u00f7 25.4 for inches \u2014 but the answers need care, because US sizes convert to non-round millimetres and ISO sizes convert to long decimals. The reliable rule is to specify in the unit the envelope was designed in: inches for #10, #9, and #6\u00be; millimetres for DL and the C and B series.<\/p>\n\n

Watch the three failure patterns: outer size is not inner capacity, a rounded figure is not exact, and postage class follows measured dimensions rather than format names. For the full size index, see our tama\u00f1os de sobre<\/a> hub, or our guide to gu\u00eda de tama\u00f1os de sobres internacionales<\/a>.<\/p>\n\n

Need a specific envelope size produced to an exact specification? Solicite una cotizaci\u00f3n<\/a> with the dimensions in the unit you want them made to.<\/p>","protected":false},"excerpt":{"rendered":"Introduction Envelope sizes are quoted in two unit systems, and neither one converts cleanly to the other. US commercial sizes were designed in inches, ISO sizes were designed in millimetres, and a conversion that looks trivial \u2014 one inch equals 25.4 millimetres \u2014 produces answers with long decimals that have to be rounded before they […]","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_metadesc":"Envelope size conversion chart \u2014 US and ISO envelope sizes in both millimetres and inches, with the conversion formula and rounding rules.","footnotes":""},"categories":[5],"tags":[],"class_list":["post-495","post","type-post","status-publish","format-standard","hentry","category-design-standards"],"_links":{"self":[{"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/posts\/495","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/comments?post=495"}],"version-history":[{"count":0,"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/posts\/495\/revisions"}],"wp:attachment":[{"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/media?parent=495"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/categories?post=495"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/envelopedock.com\/es\/wp-json\/wp\/v2\/tags?post=495"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}