Averaged length, net charge, and amino acid composition of 6676 peptides in the APD database:

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The average length of all 6676 is 28.01 residues.
The average net charge of all 6676 is 4.31

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I percent is 6.2%
V percent is 5.48%
L percent is 8.69%
F percent is 4.68%
C percent is 5.36%
M percent is 1.08%
A percent is 7%
W percent is 2.4%

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G percent is 10.28%
P percent is 4.64%

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T percent is 3.82%
S percent is 5.15%
Y percent is 2.31%
Q percent is 2.68%
N percent is 3.41%

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E percent is 2.37%
D percent is 2.24%
H percent is 2.05%
K percent is 11.86%
R percent is 8.13%

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If you want statistical information for a group of peptides, you can search the database first. Then select 'show statistic data' at the bottom of the 'query result' page.