"I do 6-8 ultrasounds a day in the office and usually the measurements of normal thyroids are 4-4.8 x 1.0-1.8 x 0.8-1.6cm which is consistent with published dimensions." - Dr Lupo (link below).
http://www.medhelp.org/posts/Thyroid-Cancer---Nodules--Hyperthyroidism/Normal-Thyroid-Size/show/263195
Based on your thyroid gland measurements, your thyroid gland is slightly enlarged. A normal thyroid gland will show an homogeneous (smooth and uniform) echotexture. A coarse echotexture means your thyroid gland is not smooth.
"However heterogeneity may persist if the chronic thyroiditis ensues [fibrosis may set in within the gland, resulting in a coarsened echotexture]". - Sonoworld - Diffuse thyroiditis
Chronic thyroiditis is another name for Hashimoto's thyroiditis. The enlargement of the thyroid gland with Hashimoto's thyroiditis is due to lymphocytic infiltration and fibrosis. Teaching manuals state Hashimoto's thyroiditis ultrasound findings as: "enlarged, hypoechoic gland with heterogenous, coarse echotexture".
Thyroid labs recommended: TSH, free T4, free T3, thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb).