A useful buttonhole setting depends on the machine method and the actual button. This calculator implements one documented method: the scale adjustment in Brother’s Sewing Guide, document cpxsg01en, pages 23–24. Select it only if that guide and foot A procedure apply to your machine. Other methods remain unknown.
At the cutting table
Buttonhole trial-length calculator
This worksheet implements the foot A scale method in the cited Brother Sewing Guide, pages 23–24. Match that document and method to your machine before calculating.
The manual’s example is a 15 mm diameter button, 10 mm thick: a 25 mm scale setting. Numbers shown are editable examples. Your entries stay in this page.
Enter your measurements to calculate.
When this particular calculation applies
The Brother Sewing Guide normally directs the reader to place the button in foot A’s guide plate. When it does not fit the plate, the guide describes adding diameter and thickness and setting the scale to that result. It states an approximate 28 mm maximum and calls for a trial buttonhole on project scrap.
Its example is a 15 mm diameter button with 10 mm thickness, giving a 25 mm scale setting. These are dimensions of a worked example, not suggested button proportions. The worksheet uses exact millimeter arithmetic; approximate inch equivalents in a manual should not be treated as exact conversions.
Start with the cited method, then test
Match the machine documentation, foot and procedure before choosing the confirmed method. Measure a round button’s diameter and thickness. Leave extra trial allowance at zero initially; use the field only when a scrap trial or applicable instruction justifies changing it. The tool checks the total against the entered foot limit, which cannot exceed the cited 28 mm ceiling. A lower limit in your own applicable instructions controls.
An answer within the limit is a proposed scrap setting, not approval to cut the garment. Sew on the actual fabric and support layers, open that trial hole carefully and check whether the real button passes and sits as intended. Stitch width, fabric thickness, interfacing and the cut opening are separate checks. This model does not estimate settings for irregular or shank buttons or extrapolate to manual, bound or other automatic buttonholes.
Length and placement are different decisions
A correct trial length does not choose where the closure belongs. Keep the pattern’s marks and overlap, then consult the button spacing guide for placement and gaps. If changing allowance on a rectangular sample, the seam worksheet shows the edge offset separately.
Method and source
This is desk research with an original arithmetic interface, not hands-on machine testing. Source checked October 15, 2026: Brother Sewing Guide cpxsg01en, pages 23–24 . No rule for another machine is inferred from the Brother brand name alone.