Work out exactly how much fabric to buy. Convert a pattern between fabric widths, and add the right amount for nap, plaid matching, and shrinkage, the things that leave you short.

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Start with the yardage your pattern lists and the width it assumes. Yardage converts it to the width of the fabric you are actually buying, then adds for anything below that applies.
The fabric amount printed on the back of your pattern envelope for your size.
The pattern assumes a fabric width. It is printed next to the yardage, often as 45 in or 60 in.
Bolt width, minus selvages. If the pattern width and this match, no conversion is needed.
Add for
Repeat size (in)
Major pattern pieces
Repeat size is the distance between matching lines in the plaid or stripe. Leave it at 0 for solid or non-matching fabric. Major pieces are the big ones like front, back, and sleeves, each needing one extra repeat to line up.
Backing needs a margin all around for quilting, and if your quilt is wider than the fabric, it seams from multiple panels. This gives you the total to buy.
The finished quilt top, side to side.
The finished quilt top, top to bottom.
Quilting cotton is usually 42 to 44 in usable.
4 in is standard for longarm. Use 2 to 3 for domestic machines.
Binding is cut in strips across the fabric, then joined into one long strip around the edge. This tells you how many strips and how much fabric.
Finished quilt, side to side.
Finished quilt, top to bottom.
2.25 to 2.5 in is typical for double-fold.
Usable width of your binding fabric, usually 42 in.
How many squares or rectangles you can cut from a piece of fabric, trying both orientations to get the most.
The fabric you are cutting from, side to side.
The fabric you are cutting from, top to bottom.
One square or rectangle you want to cut, side to side.
One piece, top to bottom.
Include your seam allowance in the piece size. A finished 4.5 in square is usually cut at 5 in.
Add each edge you are trimming and how many of it there are. Yardage totals the length, then adds for joins, corners, gathering, and a margin so you are not caught short.
Lace a decorative openwork trim, often stitched flat along a hem or edge, or gathered into a ruffle.
Trim any narrow decorative strip added to an edge. Ribbon, ric-rac, pom-pom, and piping all count.
Binding a fabric strip folded over a raw edge to enclose and finish it, common on quilts, necklines, and blankets.
A starting point you can edit. Everything below stays adjustable.
Edges to trim

An edge is any line where the trim goes: a hem, a neckline, one side of a tablecloth. Enter how long that edge is, and how many identical edges there are, like 2 sleeve cuffs.

Adjust for
Gathered trim needs more length than the edge it sits on. This is the step people most often forget.

These are buying estimates, not a cutting plan. The width conversion assumes fabric area stays about the same, which is close but not exact, since real pattern pieces do not tile perfectly onto a different width. Yardage rounds up and adds a small margin so you are not caught short, but for an expensive or hard-to-rematch fabric, buy a little extra. When in doubt, more is safer than a seam you cannot finish.