The Ultimate Guide to Nightwear Sizing: M to 3XL Explained

RS Fashion Team 24 Jun 2026 5 min read
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Nightwear sizing is meant to be about comfort, not vanity sizing, which is why we keep our size chart simple and consistent from M through 3XL.

What actually to measure

Two measurements matter most for a maxi nighty: bust (around the fullest part, keeping the tape level) and hip (around the widest part, usually a little below the natural waist). Length is the third, measured from shoulder to ankle if you prefer a specific hemline.

Reading between two sizes

If your bust and hip measurements fall into two different size rows, choose based on the bust for a fitted top portion, since the flared skirt of a maxi nighty accommodates hip variation far more easily than a fitted bodice does.

Stretch fabric changes the maths

Cotton-lycra and other stretch blends have some give built in - if a garment is listed with even 5 percent lycra, you can typically stay true to your usual size rather than sizing up.

When to size up

If you prefer a looser, more relaxed fit for sleep (rather than a closer, daywear-style fit), sizing up by one is a safe and common choice, especially in pure cotton which does not stretch.

Still unsure?

Message us on WhatsApp with your bust and hip measurement in inches and we will recommend the right size before you order.

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RS Fashion Team

RS Fashion Editorial

We write about fabric, fit and everyday comfort — so you can pick nightwear that suits your routine, your climate and your size, not just the photo.