Normal radiology reference values and measurements [2026]

Normal radiology reference values and measurements

We have compiled the normal reference values and measurements used in diagnostic radiology across all systems in one place, along with the imaging criteria for common pathologies of each organ. Every value below is referenced to a standard textbook or peer-reviewed source (see References).

This is a living document — radiology reference values differ slightly between textbooks and institutions, so the page is updated regularly. If you would like a value added or corrected, let us know in the comments.

You don't need to memorise these. Bookmark this page (Ctrl+D on Windows, ⌘+D on Mac, or the star icon on Chrome mobile) and use the quick-reference table below as a ready reckoner.

Quick reference cheat sheet (adults)

The most frequently looked-up adult upper limits of normal are collected here. Detailed, age-specific and paediatric values follow in each section.

Gastrointestinal system (GIT)

Liver

• The normal adult liver span is < 15.5–16 cm in the mid-clavicular line (craniocaudal). The average is around 14 cm.
• Liver size depends heavily on body habitus and varies widely between individuals, so an isolated "large" measurement is often a non-specific finding.
• A tongue-like inferior extension of the right lobe (Riedel lobe) is a normal variant and should not be mistaken for hepatomegaly.
• Normal liver span in neonates and children (mid-clavicular line):

A quick estimate for the upper limit of normal in children:

Upper limit of liver span (cm) = 8 + (age in years / 4)

Alternatively, the right hepatic lobe should not extend below the right costal margin in children, or more than 1 cm below it in young infants.

Gall bladder

• Normal adult gall bladder: length < 10 cm, AP (transverse) diameter < 4–5 cm.
• The gall bladder is over-distended (hydrops) when the AP diameter exceeds 4–5 cm.
• Wall thickening > 3 mm is abnormal in an adequately distended gall bladder. Do not comment on wall thickness or size when the gall bladder is collapsed (physiological post-prandial state).
• An over-distended gall bladder with wall thickening, pericholecystic fluid and a positive sonographic Murphy sign is characteristic of acute cholecystitis.
• Normal gall bladder values in neonates and children:

Biliary tree

• Common bile duct (CBD):
  • Normal diameter < 6–7 mm in adults.
  • Add 1 mm for every decade over 60 years of age.
  • Up to 10 mm can be normal in post-cholecystectomy patients.
  • In paediatric patients, 4 mm is the upper limit (and ≤ 3.3 mm in most large series).
• Normal common hepatic duct is < 5 mm.
• Intrahepatic bile ducts: < 2 mm, or less than 40% of the diameter of the adjacent portal vein.
• The cystic duct is normal up to 5 mm.

Spleen

• Normal adult splenic length < 12–13 cm (splenomegaly > 13 cm; massive splenomegaly > 20 cm).
• A quick paediatric estimate of the upper limit of splenic length: 6 + (age / 3) cm.
• Age-specific upper limits of normal splenic length (ultrasound):

Pancreas

• Normal AP diameters (they normally taper from head to tail):

The gland is normally more echogenic than, or equal to, the adjacent liver and becomes progressively more echogenic (fatty) with age. To grade the severity of acute pancreatitis on contrast CT, use the Modified CT Severity Index (CTSI) calculator.

Bowel loops & appendix

• Small bowel follows the "rule of 3s":
  • Wall thickness < 3 mm
  • Valvulae conniventes < 3 mm
  • Diameter < 3 cm
  • No more than 3 air-fluid levels

Tip: when in doubt about a bowel measurement, quoting 3 mm / 3 cm will be correct in most cases :)

• Appendix: normal outer diameter < 6 mm (< 8 mm in patients with cystic fibrosis); a compressible, non-hyperaemic appendix is normal.
• Colon: normal diameter < 6 cm; caecum < 9 cm.
• Toxic megacolon: in the appropriate clinical setting, a transverse colon diameter > 6 cm suggests toxic megacolon.
• Infantile hypertrophic pyloric stenosis:
  • Pyloric muscle wall thickness > 3 mm (the key diagnostic criterion).
  • Pyloric channel length > 15–17 mm.

Genitourinary system (GUT)

Adrenal glands

• Adult: length 4–6 cm, body thickness < 1 cm, and each limb (arm) < 3–4 mm.
• Use the adrenal washout calculator to characterise adrenal lesions on CT.
• Normal antenatal / neonatal adrenal measurements on ultrasound:

Kidneys

• Normal adult renal bipolar length 10–12 cm (upper limit ~12 cm); the left kidney is on average slightly longer than the right.
• Upper limit of normal renal volume ~140 cc.
• Normal cortical thickness > 7–10 mm; the kidney should be equally or less echogenic than the adjacent liver/spleen.
• Age-specific mean renal length in children (ultrasound):

A useful rule of thumb: renal length (cm) ≈ 4.5 + (0.35 × age in years). For Doppler indices, see the vascular section below. To characterise a renal cyst, use the Bosniak classification calculator; to score a solid renal mass for nephron-sparing surgery, use the RENAL nephrometry score calculator.

Urinary bladder

• Normal bladder wall thickness < 3 mm (distended) / < 5 mm (empty).
• Normal bladder capacity – adults: 300–500 mL; children: [(age in years + 2) × 30] mL.
• Bladder volume (mL) ≈ 0.52 × length × width × height (cm).
• Significant post-void residual (PVR) urine:
  • Adults: > 200 mL indicates inadequate emptying; > 500 mL with other features may suggest cauda equina syndrome.
  • Children: > 20 mL is considered abnormal.

Prostate

• Prostate volume > 30 cc / 30 g is considered enlarged.
• 1 cc of prostate ≈ 1 g. The two are used interchangeably, but it is better to report volume (cc), since that is what is actually measured.
• PSA density (PSAD) = serum PSA / prostate volume. A larger gland secretes more PSA, so PSA alone can mislead; PSAD is a better estimate of clinically significant disease:
  • "Omitting prostate biopsy for men with PSA-density ≤ 0.07 ng/mL² would save 19.7% of biopsy procedures while missing 6.9% of clinically significant prostate carcinoma. PSA-density cut-offs of 0.10 ng/mL² and 0.15 ng/mL² resulted in detection of 77% and 49% of Gleason Score ≥ 7 tumours" – Nordström et al., Prostate Cancer Prostatic Dis 2018.
  • The commonly quoted threshold of PSAD ≥ 0.15 ng/mL² raises suspicion for clinically significant cancer, but a lower threshold (e.g. ≤ 0.07) may be considered to avoid under-detection.
• Use the prostate volume & PSA density calculator to compute both, and the PI-RADS calculator to risk-stratify prostate mpMRI findings.

Testes

• Normal testicular volume in children < 6 years is approximately 0.3–1 mL.
• Normal adult testicular volume is approximately 15–25 mL (mean ~18–20 mL); normal size ~3–5 cm long × 2–4 cm.
• Use the radiology volume calculator to calculate testicular volume.
• Varicocele: dilated, tortuous pampiniform plexus veins > 2–3 mm in diameter; flow reversal on Valsalva suggests a higher grade.

Ovaries

• Upper limit of normal ovarian volume: 20 cc premenopausal, 10 cc postmenopausal. Mean adult ovarian volume is ~5–10 cc.
• Criteria for polycystic ovarian morphology (PCOM):
  • ≥ 20 follicles per ovary measuring 2–9 mm (2018 international / ESHRE evidence-based guideline, using high-frequency transducers ≥ 8 MHz), and/or
  • Ovarian volume ≥ 10 cc (in the absence of a dominant follicle/corpus luteum).
  • The older 2003 Rotterdam threshold of ≥ 12 follicles is still cited where high-frequency probes are unavailable.
  • Findings in one ovary are sufficient to define PCOM.
• PCOS / PCOD is a clinical diagnosis; ultrasound findings are supportive, not diagnostic on their own.
• To risk-stratify an adnexal/ovarian lesion, use the O-RADS ultrasound calculator or the O-RADS MRI calculator.

Examples of polycystic ovaries on ultrasound:

Criteria for pelvic congestion syndrome on ultrasound:

• Dilated, tortuous pelvic veins > 4 mm in diameter
• Slow blood flow (≤ 3 cm/s)
• A dilated arcuate vein in the myometrium communicating with pelvic varicosities
• Absent or reversed flow on the Valsalva manoeuvre

Uterus and endometrium

Uterine size changes dramatically across life. Normal length (and the corpus-to-cervix ratio) by life stage:

Normative uterine volume (mean, 50th centile) for ages 0–40 years (Kelsey et al.):

Endometrial thickness (double-layer, on transvaginal ultrasound):

• Postmenopausal with vaginal bleeding: abnormal if > 5 mm (biopsy indicated; 4 mm used by some).
• Postmenopausal, asymptomatic: > 11 mm warrants consideration of biopsy.
• Premenopausal thickness varies with cycle phase (thinnest post-menstrual ~4 mm, thickest secretory ~7–16 mm).
• When endometrial fluid is present, measure each layer separately and exclude the fluid.

Criteria for adenomyosis:

• Ultrasound – two or more of: indistinct endometrial–myometrial junction; asymmetric anterior/posterior myometrial thickness; sub-endometrial striations; myometrial cysts; heterogeneous myometrial echotexture; globular uterus.
• MRI – junctional zone thickness > 12 mm (8–12 mm indeterminate), or a JZ:myometrium ratio > 40%.

Cervical insufficiency / short cervix: transvaginal cervical length < 25 mm before 24 weeks in a singleton pregnancy with a prior history of preterm birth.

Vascular / Doppler ultrasound

Normal abdominal venous diameters

The most frequently queried venous calibres, in one place:

Abdominal aorta

• Normal infrarenal abdominal aorta < 3 cm (outer-to-outer wall).
• Aneurysm: diameter ≥ 3 cm, or a focal dilatation > 1.5× the expected normal segment.
• Elective repair is generally indicated when the aneurysm reaches > 5.5 cm, grows > 0.6–0.8 cm per year, or becomes symptomatic.
• For the thoracic aorta and the imaging of acute aortic syndromes, see the thoracic aorta values below and our aortic dissection article.

Renal artery stenosis (RAS) – native kidney

• Direct criteria (main renal artery):
  • Peak systolic velocity (PSV) > 180–200 cm/s – best single parameter for diagnosing/grading RAS.
  • Reno-aortic ratio (RAR) > 3.5 (PSV in stenosed renal artery / PSV in the pre-renal aorta).
• Indirect criteria (downstream, less sensitive):
  • Acceleration time > 0.07 s
  • Acceleration index < 3 m/s²
  • Side-to-side resistive index difference (ΔRI) > 0.05
  • Pulsus parvus et tardus waveform
• A resistive index > 0.8 predicts a poor response to revascularisation.

Transplant renal artery stenosis (TRAS)

• PSV at the stenosis > 2.5× the pre- or post-stenotic velocity
• PSV > 300 cm/s
• PSV (renal artery) / PSV (intralobar artery) > 13
• Acceleration time > 0.06 s

Portal venous Doppler

• Normal portal vein: ≤ 13 mm diameter, hepatopetal (towards the liver) flow, velocity 16–40 cm/s with normal respiratory variation.
• Doppler features of portal hypertension:
  • Low portal venous velocity (< 16 cm/s)
  • Hepatofugal flow (away from the liver)
  • Porto-systemic collaterals (including a recanalised paraumbilical vein)
  • Dilated portal vein > 13 mm; loss of respiratory variation in the splenic/SMV
• Normal resistive index (RI) in hepatic, splenic and renal arteries is < 0.7.
• Normal RI in the superior mesenteric artery (SMA) is > 0.8 (fasting, high-resistance waveform).

For more on the imaging spectrum of portal hypertension, see our cirrhosis & portal hypertension article, and use the resistive index (RI) calculator for any Doppler study.

Carotid Doppler – ICA stenosis criteria (updated)

Internal carotid artery (ICA) stenosis is graded by ICA peak systolic velocity (PSV) and the presence of plaque, all referenced to the NASCET method. Note the 2023 update: the Intersocietal Accreditation Commission (IAC, Nov 2023), following the Gornik et al. validation study, now recommends raising the PSV threshold for a ≥ 50% stenosis from the original 2003 SRU value of 125 cm/s to 180 cm/s, because 125 cm/s over-calls disease. The ≥ 70% threshold (> 230 cm/s) is unchanged. The current (modified-SRU / IAC 2023) criteria:

A PSV of 125–180 cm/s with an ICA/CCA ratio ≥ 2.0 and significant plaque is also consistent with a 50–69% stenosis, so all grey-scale and Doppler parameters should be weighed together. ICA PSV and plaque remain the primary parameters; the ICA/CCA ratio and ICA EDV help when PSV may be unreliable (e.g. contralateral high-grade disease, cardiac dysfunction). To convert between NASCET and ECST methods and grade a specific case, use the NASCET / ECST carotid stenosis calculator.

TIPS (transjugular intrahepatic portosystemic shunt) dysfunction

• Aliasing at the site of stenosis on colour Doppler.
• Shunt velocity > 190 cm/s at a stenotic segment, or < 90 cm/s in non-stenotic segments.
• Velocity < 30 cm/s in the main portal vein feeding the stent.
• A temporal decrease of > 50 cm/s or increase > 60 cm/s between studies suggests dysfunction.
• Absence of colour Doppler flow indicates complete occlusion.

Thorax

Trachea & airways

Thoracic aorta & great vessels

Ascending aortic aneurysm repair is generally considered at ≥ 55 mm (earlier in connective-tissue disease or bicuspid aortic valve). For acute aortic syndromes, see our aortic dissection article.

Pleura, lungs & mediastinum

• Cardiothoracic ratio (CTR): ≤ 0.5 on an erect PA chest radiograph (a higher value on AP/supine films can be spurious).
• Pleural effusion: roughly 175–200 mL is needed to blunt the costophrenic angle on an erect PA film; as little as ~50 mL may be seen on the lateral view; ~500 mL obscures the diaphragmatic contour.
• Pleura: normal visceral/parietal pleura is imperceptible; > 2–3 mm thickening is abnormal.
• Pulmonary (solid) nodule: < 3 cm by definition (≥ 3 cm = mass). Manage incidental nodules with the Fleischner Society calculator.
• Pneumothorax: estimate size and quantify with the pneumothorax volume calculator.
• Pericardial effusion: normal pericardium ≤ 2 mm; a fluid stripe > 4 mm (diastole) on echo indicates an effusion.
• Thymus: normal until ~puberty; normal thymic thickness (lobe) < 1.8 cm below age 20 and < 1.3 cm thereafter on CT.

Musculoskeletal system

Craniocervical junction & spine

Upper limb (shoulder, wrist & hand)

Pelvis & lower limb (including DDH)

Graf hip ultrasound is performed in infants (typically at 4–6 weeks); an alpha angle ≥ 60° with a beta angle < 55° is a normal (type I) hip. For skeletal maturity, use the paediatric bone age calculator.

Obstetrics

Early pregnancy & viability

• Landmarks appear in order: gestational sac (~4.5–5 weeks, mean sac diameter grows ~1 mm/day) → yolk sac → embryo with cardiac activity.
• The yolk sac should be visible once the mean sac diameter (MSD) is ≥ 8–10 mm; the embryo once MSD ≥ 16–25 mm.

Criteria for a failed / non-viable early pregnancy (Society of Radiologists in Ultrasound / NEJM, transvaginal):

A yolk sac > 6 mm, or an abnormally small/large sac relative to the embryo, is suspicious (but not diagnostic) for failure. See our summary of the NEJM early-pregnancy failure criteria.

Aneuploidy screening, amniotic fluid, cervix & placenta

Fetal biometry & Doppler

• Standard biometric parameters – biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL) – are combined (Hadlock) to estimate gestational age and fetal weight.
• First-trimester crown-rump length (CRL) is the most accurate dating measurement (± 5–7 days).
• Estimate/confirm dates with the gestational age calculator and the pregnancy due-date calculator.
• Umbilical artery Doppler: resistance falls with advancing gestation (S/D ratio < 3 after ~30 weeks). Absent or reversed end-diastolic flow is abnormal and indicates placental insufficiency.
• Middle cerebral artery (MCA): a low PI ("brain-sparing") or a raised peak systolic velocity (> 1.5 MoM, suggesting fetal anaemia) is abnormal.
• Cerebroplacental ratio (MCA-PI / UA-PI): < 1 is abnormal.

Miscellaneous

Thyroid

• Normal thyroid lobe: length 4–6 cm, width ~1.5–2 cm, and AP thickness ≤ 2 cm.
• Isthmus thickness ≤ 3–4 mm.
• Normal adult total thyroid volume ~10–15 cc (WHO upper limit ~18 mL in iodine-sufficient adults). Calculate it with the thyroid volume calculator.
• Read more about risk-stratifying thyroid nodules in our TIRADS article, and score a nodule with the TIRADS calculator.

Suggestions, feedback, and contributions are always welcome – contact us.

Reference book for normal radiology measurements

Measurements In Radiology Made Easy by Vineet Wadhwa

• A handy pocket reference covering measurements across all modalities and systems.
• You can annotate it with the values your own institution follows.

See the complete list of recommended radiology books:

Recommended Radiology Books (Updated 2022)

Frequently asked questions

What is the normal liver size in cm by age?

In adults the liver span in the mid-clavicular line is up to about 15.5 to 16 cm, with a mean around 14 cm. In a neonate the mean span is about 6.4 cm and it rises steadily through childhood. A quick upper limit of normal in children is 8 plus (age in years divided by 4) cm.

What is the normal splenic vein diameter?

The normal splenic vein measures up to 10 mm at rest and may distend with deep inspiration. For comparison, the main portal vein measures up to 13 mm and the superior mesenteric vein up to 10 mm.

What is the normal spleen size on ultrasound?

Normal adult splenic length is under 12 to 13 cm. Splenomegaly is a length over 13 cm and massive splenomegaly is over 20 cm. In children a quick upper limit of normal splenic length is 6 plus (age in years divided by 3) cm.

What is the normal testicular volume by age?

Testicular volume is about 0.3 to 1 mL in children under 6 years and about 15 to 25 mL in adults, with a mean around 18 to 20 mL. A normal adult testis measures roughly 3 to 5 cm long by 2 to 4 cm.

What is the normal uterine size by age?

Uterine length is about 2.5 to 4 cm before puberty, 6 to 8.5 cm in a nulliparous woman of reproductive age, 8 to 10.5 cm if multiparous, and typically 4 to 6 cm after menopause. The corpus-to-cervix ratio rises from 1 to 1 in childhood to 2 to 1 in adults.

What is the normal kidney size on ultrasound?

Normal adult renal bipolar length is 10 to 12 cm, with an upper limit around 12 cm and the left kidney on average slightly longer than the right. Normal cortical thickness is over 7 to 10 mm and the kidney should be equally or less echogenic than the adjacent liver or spleen.

What diameter defines an abdominal aortic aneurysm?

The normal infrarenal abdominal aorta measures under 3 cm, outer wall to outer wall. An abdominal aortic aneurysm is a diameter of 3 cm or more, or a focal dilatation over 1.5 times the expected normal segment. Elective repair is generally considered once the aneurysm reaches about 5.5 cm.

References

• Rumack & Levine. Diagnostic Ultrasound (textbook)
• The Radiology Assistant – Normal Values Ultrasound (paediatric)
• OHSU – Paediatric Radiology Normal Measurements
• Grant et al. Carotid Artery Stenosis: Gray-Scale and Doppler US Diagnosis – SRU Consensus Conference. Radiology 2003
• Gornik et al. Optimization of duplex velocity criteria for diagnosis of ICA stenosis (IAC Carotid Diagnostic Criteria Committee). Vascular Medicine 2021 & IAC Updated Recommendations for Carotid Stenosis Interpretation Criteria (Nov 2023)
• Doubilet et al. Diagnostic Criteria for Nonviable Pregnancy Early in the First Trimester. NEJM 2013
• MacMahon et al. Guidelines for Management of Incidental Pulmonary Nodules – Fleischner Society 2017. Radiology 2017
• Kelsey et al. A Validated Normative Model for Human Uterine Volume from Birth to Age 40 Years. PLOS ONE 2016
• Dewailly et al. / 2018 international evidence-based PCOS guideline (polycystic ovarian morphology criteria)
• Nordström et al. PSA density in the diagnostic algorithm of prostate cancer. 2018
• Radiologic Assessment of Native Renal Vasculature: A Multimodality Review. RadioGraphics 2017
• Emamian et al. Kidney dimensions at sonography in 665 adult volunteers. AJR 1993
• Bladder Post-Void Residual Volume (StatPearls)

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