The beta calculator using the info below is now online:
http://www.browneyedbabsknits.com/yarn-substitution-calculator.html

To help estimate yardages I’m working up a few swatches in different weights of yarn to a tight gauge (suitable for toys) and weighing them to estimate the yardage in each swatch. This should give me a ratio for estimate yardage for a toy worked in a different yarn.

Fingering - Posh - 3.25mm/US 3 (not quite tight enough gauge)
900 stitches = 4g / 14.4 yards
100 stitches = 1.6 yards; 4” square = 25 sts x 36 rows

Fingering - Spindrift - 2.75mm/US 2
900 stitches = 3g / 13.8 yards
100 stitches = 1.5 yards; 4” square = 28 sts x 40 rows

Fingering held doubled - spindrift - 3.5mm/US 4
400 stitches = 4g / 18.4 yards
100 stitches = 4.6 yards; 4” square = 22 sts x 35 rows

WYS DK held single - 3.5mm/US 4
400 stitches = 3g / 7.6 yards
100 stitches = 1.9 yards; 4” square = 22 sts x 36 rows

Swish DK held single - 3.5mm/US 4
400 stitches = 4g / 9.8 yards
100 stitches = 2.45 yards; 4” square = 24 sts x 32 rows

Wendy DK held single - 3.5mm/US 4
400 stitches = 2g / 5.2 yards
100 stitches = 1.3 yards; 4” square = 24 sts x 36 rows

DK fun fur - 3.5mm/US 4
400 stitches = 4g / 7.8 yards
100 stitches = 1.95 yards; 4” square = 27 sts x 36 rows

WYS DK held double - 4mm/US 6
400 stitches = 8g / 20.2 yards
100 stitches = 5.05 yards; 4” square = 19 sts x 28 rows

Aran - 4mm/US 6
400 stitches = 5g / 9.8 yards
100 stitches = 2.45 yards; 4” square = 18 sts x 30 rows

Light super Bulky - 5mm/US 8
400 stitches = 6g / 11.5 yards
100 stitches = 2.9 yards; 4” square = 15 sts x 22 rows

Super Bulky - 5mm/US 8
400 stitches = 14g / 13.7 yards
100 stitches = 3.43 yards; 4” square = 15 sts x 22 rows

Textured Super bulky - 6mm/US 10
400 stitches = 34g / 15 yards
100 stitches = 3.75 yards; 4” square = 10 sts x 13 rows