How do I know if shoulder width needs adjusting?

The shoulder seam should sit at the point of your shoulder (the bony bump). If the seam sits on your arm, the shoulders are too wide. If it digs into the top of your arm, they are too narrow.

How do I adjust shoulder slope?

Shoulder slope is adjusted at the armhole end of the shoulder seam. For sloping shoulders, lower the shoulder point. For square shoulders, raise it. This also affects the armhole and may need a corresponding sleeve adjustment.

Can I narrow broad shoulders on a finished garment?

Yes, by taking a deeper seam at the shoulder point and tapering to nothing at the neckline. This narrows the shoulder while maintaining the neckline position. You may need to adjust the sleeve head to match.

How does shoulder adjustment affect sleeves?

Changing the shoulder width or slope changes the armhole shape and size. The sleeve cap may need adjusting to fit the new armhole. Check the sleeve ease (usually 2-4cm) after adjusting the bodice shoulders.

Shoulder Adjustment Calculator — Free Alterations Tool

Shoulder Adjustment Calculator — Width & Slope

Calculate shoulder width and slope adjustments.

Adjustment TypeWidth reshapes how far the seam sits across the body; slope raises or lowers the shoulder point

Current Shoulder Width

Across back, shoulder point to shoulder point

Desired Shoulder Width

Target across-back width (shoulder to shoulder)

Current Shoulder Slope

Drop from neck point to shoulder point

Desired Shoulder Slope

Target drop from neck point to shoulder point

How We Calculate This

Across-back width spans both shoulder seams, so the total change is divided equally between them — each bodice piece (cut on the fold) takes half. Width is moved at the armhole end of the shoulder seam; slope raises or lowers the shoulder point at that same end.

A width move kept under about 2 cm per shoulder reshapes only to the armhole seamline, leaving the armscye length — and the sleeve — unchanged. The slope change is what alters armscye height, so the indicative sleeve-cap figure keys off the slope adjustment; lower (or raise) the armhole by the same amount to keep the armscye length, then re-true the sleeve cap.

The formula

Width adjustment = Desired - Current width

Per shoulder = Width adjustment ÷ 2

Slope adjustment = Desired slope - Current slope

Sleeve cap (indicative) = |Slope adjustment| × factor

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Always verify quantities before cutting or purchasing fabric.

Shoulder Adjustment Calculator — Width & Slope

How We Calculate This

The formula

Frequently Asked Questions

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