参考値です。
LocalPrintServer.DefaultPrintQueue.GetPrintCapabilities().PageMediaSizeCapabilityにて取得しました。
ISOA0 (3178.56 x 4493.76)
ISOA1 (2245.44 x 3178.56)
ISOA2 (1587.40157480315 x 2245.03937007874)
ISOA3 (1122.51968503937 x 1587.40157480315)
ISOA4 (793.700787401575 x 1122.51968503937)
ISOA5 (559.370078740158 x 793.700787401575)
ISOA6 (396.850393700787 x 559.370078740158)
ISOC5Envelope (612.283464566929 x 865.511811023622)
ISODLEnvelope (415.748031496063 x 831.496062992126)
ISOSRA3 (1209.52062992126 x 1700.79874015748)
JISB4 (971.338582677165 x 1375.74803149606)
JISB5 (687.874015748032 x 971.338582677165)
JapanChou3Envelope (453.543307086614 x 888.188976377953)
JapanChou4Envelope (340.157480314961 x 774.803149606299)
JapanDoubleHagakiPostcardRotated (559.370078740158 x 755.905511811024)
JapanHagakiPostcard (377.952755905512 x 559.370078740158)
JapanYou4Envelope (396.850393700787 x 888.188976377953)
NorthAmericaArchitectureBSheet (1152.72188976378 x 1727.28188976378)
NorthAmericaExecutive (696 x 1008)
NorthAmericaGermanLegalFanfold (816 x 1248)
NorthAmericaLegal (816 x 1344)
NorthAmericaLetter (816 x 1056)
NorthAmericaMonarchEnvelope (372 x 720)
NorthAmericaNumber10Envelope (396 x 912)
NorthAmericaNumber9Envelope (372 x 852)
NorthAmericaStatement (528 x 816)
NorthAmericaTabloid (1056 x 1632)
OtherMetricA4Plus (793.700787401575 x 1247.24409448819)
使い易いように、CSVでも出力しました。列： PageMediaSizeName,Width,Height
ISOA0,3178.56,4493.76
ISOA1,2245.44,3178.56
ISOA2,1587.40157480315,2245.03937007874
ISOA3,1122.51968503937,1587.40157480315
ISOA4,793.700787401575,1122.51968503937
ISOA5,559.370078740158,793.700787401575
ISOA6,396.850393700787,559.370078740158
ISOC5Envelope,612.283464566929,865.511811023622
ISODLEnvelope,415.748031496063,831.496062992126
ISOSRA3,1209.52062992126,1700.79874015748
JapanChou3Envelope,453.543307086614,888.188976377953
JapanChou4Envelope,340.157480314961,774.803149606299
JapanDoubleHagakiPostcardRotated,559.370078740158,755.905511811024
JapanHagakiPostcard,377.952755905512,559.370078740158
JapanYou4Envelope,396.850393700787,888.188976377953
JISB4,971.338582677165,1375.74803149606
JISB5,687.874015748032,971.338582677165
NorthAmericaArchitectureBSheet,1152.72188976378,1727.28188976378
NorthAmericaExecutive,696,1008
NorthAmericaGermanLegalFanfold,816,1248
NorthAmericaLegal,816,1344
NorthAmericaLetter,816,1056
NorthAmericaMonarchEnvelope,372,720
NorthAmericaNumber10Envelope,396,912
NorthAmericaNumber9Envelope,372,852
NorthAmericaStatement,528,816
NorthAmericaTabloid,1056,1632
OtherMetricA4Plus,793.700787401575,1247.24409448819
数値の単位がよく分かっていません。大体、96dpiでのピクセル数?という感じがするのです。
ILSpyで調査しました所、寸法(μm) ÷ 25400 × 96.0 で計算するようです。A4縦の幅の場合、210000/25400*96→793.7007874015748
(ReachFramework, MS.Internal.Printing.Configuration.UnitConverter.LengthValueFromMicronToDIP)
Note: 個人的に使う余白値 Margin="20"
