Crochet projects can involve material estimates, gauge measurements, compatible stitch counts, and round-by-round arithmetic. The needed model depends on the actual construction, so each calculator states the inputs and limits it supports instead of inferring a whole project.
FiberTools crochet calculators use the inputs and arithmetic models stated on each page. The yarn calculator scales yarn length actually consumed by a representative swatch to a flat rectangle; it does not infer consumption from stitch gauge or choose a hook. The gauge calculator compares measured proportions and counts, but it cannot prescribe an exact hook change because yarn, stitch pattern, technique, and maker tension also affect the fabric. Blanket sizes use nominal presets and measured-swatch inputs. Its displayed 10% planning allowance is part of the model, not a measurement of borders, joins, or every source of waste.
The construction tools provide bounded arithmetic references for their displayed models. The amigurumi and circle tools generate basic count schedules that still require a suitable pattern and physical sample. The granny square planner rounds a target up to a nominal grid, counts unique internal seam distance, and can scale measured yarn per square; it does not infer joining yarn or guarantee finished dimensions.
Treat each result according to the inputs and limitations shown by that tool. Rounded counts, nominal dimensions, and measured-input yarn scenarios are planning references rather than exact finished-size or purchase guarantees. Every self-service calculator listed here is free. Optional professional reviews and project downloads are separate paid offers.