When to Size Up and When to Size Down

The dominant sizing advice for activewear is to size down for compression. This is wrong for anyone whose shape falls outside the size block the brand graded from, and it is wrong more often than most people assume.

Start with the fabric, not the number

A high-compression knit has enough give to fit comfortably across a small range of sizes. A mid-weight smooth knit has less. Structured fabrics have less still. Sizing down only works when the garment has enough stretch to accommodate the difference.

If you are between sizes on a structured legging, the size down will fit. It will also restrict, because structured fabric does not extend as much as it needs to. You will feel this first in a deep lunge.

BRAS

Airlift Intrigue Bra

$31$78

SHOP THIS STYLE

When sizing down works

• High-compression leggings with at least 20 percent elastane
• Sports bras with an adjustable band and a molded cup
• Shorts with a bonded or narrow waistband
• Any garment where you are genuinely between sizes rather than a full size out

When sizing up is the correct answer

• Structured or mid-weight smooth fabrics
• Any garment where the size range at your waist is wide
• Styles with a contoured or bonded waistband that is designed to sit snug
• When the alternative is a rise mismatch, which no size change fixes

The sports bra calculation is different

A bra size has two independent variables: the band and the cup. Sizing down on the band while keeping the cup means a band that will not hold under movement. Sizing up on the band while keeping the cup means a band that sits too high.

The correct adjustment is usually to size up the band and keep the cup, then use the adjustable component to close the gap. If a bra does not have an adjustable band, buy the size that fits the cup and plan for a slight looseness at the band.

A fitting protocol that takes five minutes

1. 01Buy two sizes of the same style, in the same color, if possible
2. 02Wear each for five minutes of actual movement, not just standing
3. 03In each size, test the hardest position for your practice
4. 04Check the waistband under load, not at rest
5. 05Keep whichever size you did not choose, because it is a reference point

Fit is not a number on a label. It is a garment behaving predictably in the positions where you actually move.

What to check before you buy for when size up when size down

Two pieces can look identical on the hanger and behave differently in when size up when size down. The checks below are the ones that catch it early. Emerald Isle ALO Softsculpt Precision Bra is the piece we would test them against first.

• The band should sit level front and back and stay put when you lift your arms.
• Jump once: if there is vertical movement the band is too loose, not the straps.
• Check the strap join — a narrow join digs in after twenty minutes.

What to ignore

Ignore comparative sizing between brands. A medium in one brand and a medium in another may have entirely different dimensions, and the conversion charts are approximations produced by people who have not tried either garment.

Only the garment on your body tells you anything. This is the least enjoyable fact about online clothing shopping, and it is why the return policy matters more than the size chart.