Not entirely. Numbered sizes vary by region and brand, so relying purely on the number may result in a poor fit. For instance:

• An EU 38 may correspond to a UK 10, but it could still have slightly different measurements depending on the brand.
• A US 8 may map to UK 12 but fabric and cut may affect how it fits.
  Using the size conversion chart and your actual bust/waist measurements gives the best chance of a good fit

The EU standard EN 13402 (which bases size labels on body dimensions in cm) is intended to harmonize clothing sizes across Europe. Wikipedia However, while it is recognized, adoption in the UK and by many brands is inconsistent. So while it is a useful reference, you should not rely on it as an absolute standard for every garment or brand.

European (EU) sizes are commonly two size-steps ahead of UK sizes — for example, an EU 38 typically equals UK 10. The EU sizing system tends to use body measurements in centimetres and then label garments accordingly.
Because each brand may interpret the size differently, it’s important to check the waist and bust measurements (in cm) when converting EU → UK.

Key measurement steps:

• Bust: Measure around the fullest part of your bust, keeping the tape level and snug but not tight.
• Waist: Measure around the narrowest part of your body, usually just above the belly button.
• Hips (if relevant): Measure around the fullest part of your hips.
  Use these real measurements to match against the size chart (for EU, UK, or US) rather than going by the size label alone

If your measurements fall between two sizes:

• Choose the larger size for comfort, especially if the fabric is non-stretch or you prefer looser fit.
• Choose the smaller size if the garment is made of stretch fabric or you like a snug fit.
  Since online sizing conversion is not always perfect, opting for a size up gives you flexibility and less chance of being too tight.

In general, US women’s sizes are typically one size smaller than their UK equivalents. For example, a US 6 often corresponds to a UK 10. This is because size-labelling conventions differ: US sizes are usually based on bust/waist in inches, whereas UK sizes follow a different measurement system.
When shopping from US brands into the UK, always check your bust/waist measurements and match them to a UK size chart rather than relying purely on the numbered size label.

When shopping from US sites and shipping to the UK:

• Convert the US size to the equivalent UK size (using the chart you have).
• Check if the garment uses inches (US standard) or cm (EU/UK standard) for sizing details.
• Account for shipping/returns — if returns are difficult or expensive, favour a brand with a clear size chart and liberal return policy.
• Consider any duty/taxes when shipping internationally from US to UK.
  By taking these steps, you reduce the risk of ordering the wrong size and having to return.

Even if you select the correct converted size, poor fit can still happen because:

• The cut or style (slim, relaxed, oversized) may differ from your expectations.
• The brand’s sizing may not conform exactly to the conversion chart — for example, a “UK 12” in one brand may actually fit closer to what another brand labels “UK 14”.
• Fabric type matters: A rigid, non-stretch fabric will behave differently than a stretchy one.
  To mitigate this: check the fabric composition, review product photos and sizing notes, and if possible check customer reviews about fit.

Several factors cause variation in size charts:

• Brands may use different body measurement standards or fit models.
• Fabric types (stretch vs rigid) affect how a garment fits.
• “Vanity sizing” (labels making garments appear smaller) influences sizing across brands.
  Because of this, the same “UK 10” may fit differently in two brands. Always refer to the brand’s specific size chart and compare your own measurements.

EU sizes are often based on body measurements in centimetres and labelled accordingly. Wikipedia+1

US sizes often use inches for bust, waist, hips.

UK uses a mix (but common female charts will cite inches for bust/waist).
As a result, confusion arises if shoppers don’t convert units. Always check whether the measurement is in cm or inches, and if necessary convert (1 inch ≈ 2.54 cm).