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# How to calculate a check digit manually

ID Key Format Digit positions
GTIN-8                     N1 N2 N3 N4 N5 N6 N7 N8
GTIN-12             N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12
GTIN-13           N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13
GTIN-14         N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14
GSIN   N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14 N15 N16 N17
SSCC N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14 N15 N16 N17 N18
Step 1: Multiply value of each position by
x3 x1 x3 x1 x3 x1 x3 x1 x3 x1 x3 x1 x3 x1 x3 x1 x3
Step 2: Add results together to create sum
Step 3: Subtract the sum from nearest equal or higher multiple of ten = Check Digit

### The following table gives an example to illustrate how a GTIN-13 Check Digit is calculated:

ID Key Format N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13
Number without Check Digit 6 2 9 1 0 4 1 5 0 0 2 1 -
Step 1: Multiply x x x x x x x x x x x x -
by 1 3 1 3 1 3 1 3 1 3 1 3 -
Step 2: Add results = = = = = = = = = = = = -
to create sum 6 6 9 3 0 12 1 15 0 0 2 3 =57
Step 3: Subtract the sum from nearest equal or higher multiple of ten = 60- 57 = 3 (Check Digit)
Number with Check Digit 6 2 9 1 0 4 1 5 0 0 2 1 3