GAP and Primark don't just fit differently — they count differently. GAP sizes in US numeric and alpha sizes; Primark labels everything in UK sizing, which runs four numbers higher than US (a Primark 12 is a US 8). So the first job when switching between them is conversion, and the second is adjusting for two very different fit reputations.
GAP runs true to size by US standards, leaning slightly generous, with a relaxed classic American cut. Primark tends to run small — most sharply in jeans, fitted dresses, and tailored shirts — and its garment-to-garment consistency is famously loose, to the point that Primark revised its size chart in 2021 after complaints. Below, both charts aligned by body measurement, because the size labels alone won't get you there.
The short answer
Primark runs smaller — GAP is true to size while Primark's fitted styles commonly need a size up
The fit verdicts point in opposite directions: GAP is true to size leaning roomy, while Primark runs small overall, worst in denim, fitted dresses, and tailored shirts — even Primark staff are known to recommend sizing up in jeans. So for the same body, the GAP piece in your chart size will fit as expected, while the equivalent fitted Primark piece is usually safer one size up.
The charts add a wrinkle: the two brands' US numbers don't line up consistently. At the small end, Primark's nominal US size covers a smaller body than GAP's same number — a Primark US 4 charts an 83 cm bust where GAP's 4–6 covers 87.5–90 cm — and the charts only converge around US 12. Skip the label arithmetic entirely and match your bust and waist measurements to each chart, then apply Primark's size-up rule for anything fitted.
GAP vs Primark at a glance
| GAP | Primark | |
|---|---|---|
| Sizing system | US numeric + alpha sizes | UK sizing — runs four numbers higher than US |
| Fit verdict | True to size, leaning slightly generous | Runs small — sharpest in jeans, fitted dresses, tailored shirts |
| Where to adjust | Size down in relaxed and oversized styles | Size up in denim and anything fitted |
| Consistency | Fit drifts between items and seasons | Famously loose — two identical garments can fit differently |
| Chart history | Stable published chart | Chart revised in 2021 after runs-small complaints |
Primark sizes mapped to GAP sizes (women)
Aligned by body bust measurement, not by label — the brands use different size systems, and their US numbers don't correspond to the same bodies. Primark publishes in cm with inches converted.
| Primark UK | Primark US | Primark bust | Closest GAP size | GAP bust |
|---|---|---|---|---|
| 8 | 4 | 83 cm · 32.5" | XS (0–2) | 32.5–33.5" · 82.5–85 cm |
| 10 | 6 | 87 cm · 34.5" | S (4–6) | 34.5–35.5" · 87.5–90 cm |
| 12 | 8 | 91 cm · 36" | S–M | 34.5–35.5" · 87.5–90 cm / 36.5–37.5" · 92.5–95.5 cm |
| 14 | 10 | 96 cm · 38" | M–L | 36.5–37.5" · 92.5–95.5 cm / 39–40.5" · 99–103 cm |
| 16 | 12 | 102 cm · 40" | L (12–14) | 39–40.5" · 99–103 cm |
| 18 | 14 | 109 cm · 43" | XL (16–18) | 42–44" · 106.5–112 cm |
Women's waists side by side
Aligned by body waist measurement — GAP sizes matched to the nearest Primark UK size. Note the waist alignment lands a notch higher than the bust alignment above; the two brands grade proportions differently.
| GAP size | GAP waist | Closest Primark UK | Primark waist |
|---|---|---|---|
| XS (0–2) | 25.5" · 65 cm | 8 | 66 cm · 26" |
| S (4–6) | 26.5–27.5" · 67.5–70 cm | 10 | 70 cm · 27.5" |
| M (8–10) | 28.5–29.5" · 72.5–75 cm | 12 | 74 cm · 29" |
| L (12–14) | 30.75–32" · 78–81.5 cm | 14 | 79 cm · 31" |
| XL (16–18) | 33.75–35.75" · 85.5–91 cm | 16 | 85 cm · 33.5" |
| XXL (20) | 37.75" · 96 cm | 18–20 | 94 cm · 37" / 97 cm · 38" |
Men's tops side by side
GAP lists body chest; Primark lists to-fit chest and states its men's sizes are the same across UK, EU, and US. From M upward Primark's letters chart about an inch smaller than GAP's.
| Size | GAP chest | Primark chest |
|---|---|---|
| XS | 34–36" · 86.5–91.5 cm | up to 36" · 90 cm |
| S | 36–38" · 91.5–96.5 cm | 36–38" · 91–96 cm |
| M | 39–41" · 99–104 cm | 38–40" · 97–102 cm |
| L | 42–44" · 106.5–112 cm | 41–43" · 103–108 cm |
| XL | 45–47" · 114.5–119.5 cm | 44–46" · 112–117 cm |
| XXL | 48–50" · 122–127 cm | 47–49" · 119–124 cm |
Switching between GAP and Primark
- Don't convert by label — match your bust and waist to each chart. The brands' US numbers describe different bodies at the small end and only converge around US 12.
- At Primark, size up in jeans, fitted dresses, and formal shirts; basics and oversized styles are closer to true to size.
- At GAP, keep your true size in classic fits and size down in relaxed and oversized lines — the opposite instinct from Primark.
- Because Primark's garment-to-garment consistency is loose, check the measurements on the label of the actual garment, not just the size — two copies of the same piece can measure differently.
Measurements are based on each brand's published size charts and may vary by garment, fabric, and region. For the full charts and fit notes, see the GAP size guide and the Primark size guide.
GAP vs Primark sizing FAQs
Which runs smaller, GAP or Primark?
Primark, clearly. GAP runs true to size by US standards and even leans slightly roomy, while Primark tends to run small — worst in jeans, fitted dresses, and tailored shirts, where sizing up one is standard advice. Primark's loose garment-to-garment consistency adds extra variance on top.
What Primark size am I if I wear a GAP medium?
By waist, a GAP M (28.5–29.5") lines up with a Primark UK 12 (74 cm · 29"). That's the chart answer — for Primark jeans, fitted dresses, or tailored shirts, the brand's runs-small tendency means the UK 14 is often the safer buy.
Is a Primark US size the same as a GAP US size?
No. Primark's converted US numbers chart smaller bodies than GAP's at the small end — a Primark US 4 covers an 83 cm bust where GAP's 4–6 covers 87.5–90 cm — and the two only converge around US 12. Treat Primark's US column as a rough conversion of its UK sizing, not as GAP-equivalent.
Why is Primark less predictable than GAP?
Primark's manufacturing tolerances vary across factories and batches, so two identical items in the same size can measure differently — a known quirk the brand's 2021 chart revision didn't fully fix. GAP has its own consistency complaints, but they're about fit drifting between styles and seasons, not between copies of the same garment.
Do GAP and Primark men's letter sizes match?
Roughly at S, then they drift: from M upward Primark's letters chart about an inch less chest than GAP's (Primark M is 38–40" vs GAP's 39–41"). If you're at the top of your GAP letter, take the next letter up at Primark.
