Google Chart API の制限事項まとめ

日本語で書かれているものもあったけど、ドキュメントみたら古かったので最新版(2011-10-25時点)をまとめておく。

1日の回数制限は無し

http://code.google.com/intl/ja/apis/chart/image/docs/making_charts.html
Google Chart Usage Policy
There's no limit to the number of calls per day you can make to the Google Chart API. However, we reserve the right to block any use that we regard as abusive.

GETの場合は、2K(2048byte) まで

http://code.google.com/intl/ja/apis/chart/image/docs/making_charts.html#creatingbyhand
Use GET or POST to get your image.
GET, is either when you type the URL directly into your browser, or use it in an tag. However, URLs are limited to 2K in length, so if you have more data than that, or have a taste for blood, you should consider using POST instead

画像サイズは、縦横の合計が30万pixel以内、縦横それぞれ最大の長さは1000pixel まで

http://code.google.com/intl/ja/apis/chart/image/docs/chart_params.html#gcharts_chs
Maximum chart size for all charts except maps is 300,000 pixels total, and maximum width or length is 1,000 pixels. Maximum size for maps is 440x220.

昔は一日250,000回という制限があったらしいけど、今は実質無制限みたい。