Hi Lee,
here are some average dimensions:
whole Length: 40 - 100 cm (16-40 inch)
Blade length: 30 - 80 cm ( 12-32 inch) (short Sax = 20 - 25 cm)
Blade width: 3 - 6.5 cm (1.2- 2.6 inch)
Blade thickness: 0.6 - 0.8cm (1/4-1/3 inch)
I hope, this will help. The german Wikipedia-article is pretty detailed. If you need more informations from this article (with some historical dates and also the archaeometallurgical background), I can try to translate it for you.
I added a picture of a Sax with some runes (
https://en.wikipedia.org/wiki/Seax_of_Beagnoth).