What size baby clothes should I buy from an ultrasound weight?

What is the number on a growth scan, if it is not a clothes size?

On a third-trimester growth scan, the sonographer measures head circumference, abdominal circumference and femur length. NHS trust leaflets (for example University Hospitals Sussex and Gateshead Health) explain that those measurements produce an estimated weight, plotted on a growth chart to watch the pattern. That estimate is for antenatal care. It is not the weight written in the notes after birth, and it is not a hanger size.

NICE NG201 evidence on monitoring fetal growth records that ultrasound is not a precise predictor of whether a baby will be small or large. This page does not add a homemade accuracy percentage. The useful clothes rule is: do not treat the scan grams as a birth weight.

If the scan raises a clinical concern, that belongs with the midwife or obstetric team. Clothes shopping does not interpret an EFW centile.

How should I shop if I only have a scan weight?

The NHS list of what to buy for a newborn is a short starter kit (sleepsuits, vests, cardigans). It never maps a scan weight onto Newborn versus 0–3. NCT is blunt: size is not known until birth.

1. 1
   Buy two bands, not one prophecy A few Newborn or First Size pieces plus more Up to 1 month / 0–3 months covers both a lighter birth and a 4kg-plus baby. This is a receipt strategy, not a medical plan.
2. 2
   Read each brand's kg and cm Mamas & Papas Newborn ends at 3.2kg / 50cm. Next First Size ends at 3.4kg / 50cm. John Lewis Newborn runs to 4.1kg / 56cm. A scan of "about 3.6kg" is already past two of those labels and still inside the third — if the birth weight even matches.
3. 3
   Keep tags and receipts Unopened packs can go back once the midwife has written the real weight. Do not fill every drawer from one EFW.
4. 4
   Size from the weighed baby After birth, match the notes weight and a crown-to-heel cm to the chart. Retire the unused band.

If the scan looks big, should I skip Newborn altogether?

Skip filling the Newborn drawer, not the last two vests. A "large" EFW can still arrive under 4.1kg and wear John Lewis Newborn. The same EFW can arrive over 4.1kg and need 0–3 on that chart from day one. Next First Size (3.4kg) is the label a larger birth is most likely to skip; John Lewis Newborn is the label that still has headroom.

If the scan looks small, should I buy only Tiny Baby?

No. Tiny Baby on John Lewis is up to 3.1kg and 50cm; Next 5lb is 2.3kg. Those labels are for a measured small baby, not for a scan story. A "small" EFW can still clear 3.2kg at birth and skip Mamas & Papas Newborn. Keep Tiny Baby / First Size as a short pile and put everyday volume in Newborn and 0–3 until the scales have been used.

When do I throw the scan weight away for shopping?

As soon as there is a birth weight. From that point the scan grams are antenatal history. Use the notes weight, a home crown-to-heel cm for the chart (not for plotting a centile), and the brand size guide. Gifts bought from the EFW can stay if they still match; return the rest while tags are on.

In shortEFW is a scan estimate from head, tummy and thigh measurements. It is not a birth weight and not a size. Two bands, keep receipts, then dress from the weighed baby and the brand's kg/cm chart.

Can clothes shopping tell me whether the scan was "right"?

No. A sleepsuit that fits or does not fit does not confirm or overturn a growth-scan plot. Questions about the estimate itself go back to the team who ordered the scan. This page only stops the estimate being used as a single clothes size.