相片大小, 2R, 3R, 4R? (Photo Printout Size, 2R, 3R, 4R?)

------想曬相, 想印相, 可以看看有甚麼選擇------

2R = 2.5″ X 3.75″(?) (63.5 × 95.25 mm)(?)
3R("9 × 13 cm") = 3.5″ X 5″ (89 × 127 mm)
4R("10 × 15 cm") = 4″ X 6″ (102 × 152 mm)
5R("13 × 18 cm") = 5″ X 7″ (127 × 178 mm)
6R = 6″ X 8″ (152 × 203 mm)
8R = 8 X 10″ (203 × 254 mm)
16R = 16″ X 20″


表示相片尺寸的「R」制度(2R, 3R, 8R等等)是怎樣計算的?

基本上，無論橫度定直度，長闊比例大概是3:2，這就是每張135菲的比例 (36mm x 24mm) (多謝讀者Vincent指正)。R前面的數字是較短一邊的尺寸(英吋做單位)，所以4R就應該係4″ X 6″，5R就應該係 5″ X 6.6665″，但由於計起來長的一邊未必是整數，相紙製造商就round up/down尺寸，久而久之大家公認了這標準。
其實2R和3R短的一邊分別係2.5″同3.5″，但為了方便只稱為2R和3R，而不是2.5R和3.5R。

Photo print sizes - Wikipedia, the free encyclopedia

They are often denoted with a code of the format nR, where the number n represents the length of the shorter edge in inches. In the normal series, the long edge is the length of the short edge plus 2 inches (10" or less) or 3 inches (11" and above).

http://www.fotomaxonline.com/help_tc.htm

Product	Image Size (Inch)	The Best Resolution (Pixels)	Minimum Resolution (Pixels)
1.5"x2" ID Photo 8 pcs	1.5 x 2	450 x 600	270 x 360
2R	2.5 x 3.5	750 x 1050	450 x 630
3R	3.5 x 5	1050 x 1500	630 x 900
4D (4.5"x6")	4.5 x 6	1350 x 1800	810 x 1080
4R	4 x 6	1200 x 1800	720 x 1080
5R	5 x 7	1500 x 2100	900 x 1260
6R	6 x 8	1800 x 2400	1080 x 1440
8R	8 x 10	2400 x 3000	1440 x 1800
8F	8 x 12	2400 x 3600	1440 x 2160
Photo Mouse Pad	6 x 8	1800 x 2400	1080 x 1440
Photo Mug	3 x 5.25	900 x 1575	540 x 945
4R 3D Photo with Frame	4 x 6	1200 x 1800	720 x 1080
Aluminum Bottle 600ml	3 x 5.25	900 x 1575	540 x 945
Aluminum Sport Bottle 400ml	3 x 5.25	900 x 1575	540 x 945
Softy Cushion	8.25 x 11.68	2475 x 3504	1485 x 2103
Multi-purposes Shoulder Bag	7.5 x 10.5	2250 x 3150	1350 x 1890
Puzzle 120pcs w/ Frame	7.7 x 11.4	2310 x 3420	1386 x 2052
Metal Compact Mirror	2.36 x 2.36	708 x 708	425 x 425
Metal Card Holder	1.93 x 3.46	579 x 1038	348 x 623
Laser Crystal Glass Key Ring	2.5 x 2.5	700 x 700	450 x 450
A3 Poster	12 x 16.5	2400 x 3300	-

------想曬相, 想印相, 可以看看有甚麼選擇------