A swatch-based yarn estimate depends on measured fabric density: how much yarn weight covers a given area. If the sample’s area or weight changes, the estimate changes even when the blanket dimensions stay the same.
Compare two samples
Imagine two 5 g samples. The first measures 10 × 10 cm, giving 0.05 g per cm². The second measures 11 × 11 cm, giving about 0.0413 g per cm². Scaled to a 100 × 120 cm blanket, the base estimates are 600 g and approximately 495.9 g.
This is a mathematical illustration, not a claim that changing a hook will produce either sample. The larger measured area spreads the same sample weight over more fabric. That is why you should use your own measurements for the intended stitch and yarn.
Keep comparisons like for like
Measure samples in a comparable prepared state. Check that the swatch represents the blanket body rather than a decorative border or a different stitch section. Weigh the part whose dimensions you measured: combining an interior area measurement with the weight of a larger piece overstates density.
The Craft Yarn Council’s crochet gauge guidance recommends making a sample in the specified yarn, hook and stitch and checking the resulting gauge. Our tools use that measured sample to estimate quantities; they do not predict the result of a hook change.
A larger allowance does not repair a wrong input
If the calculator’s result looks surprising, check units, dimensions, net swatch weight and label values first. An arbitrary extra percentage can hide a unit error. Once the measurements are sound, choose an allowance that reflects how much uncertainty you want to accommodate.
Recalculate with the blanket yarn calculator, or follow the complete worked example. These estimates have mathematical tests, but have not been validated by completing physical blankets.
Use the calculator ↗Examples illustrate the arithmetic; they are not physical project tests. Send a correction.