Foley Catheter Size Calculator

The French Size System Explained:

• French size (Fr or Ch) measures circumference, not diameter. Each French unit equals approximately 0.33mm in diameter. Here's what the colours mean:

Green (12-14Fr)

• Best for: Routine drainage, post-operative monitoring
• Flow rate: Good for clear urine without sediment
• Patient comfort: Minimal urethral irritation

Red (16-18Fr)

• Best for: Urinary retention, thicker urine
• Flow rate: Handles debris and mild sediment
• Patient need: Faster drainage in obstruction cases

Purple (20-22Fr)

• Best for: Haematuria, blood clots, irrigation 
• Flow rate: Maximum drainage for challenging cases
• Clinical setting: Usually urology or post-TURP

Paediatric Sizing Rules - Children aren't small adults - their urethral anatomy changes dramatically with age:

• Infants (0-2 years): 5-8Fr (specialist only)
• Children (2-12 years): 8-12Fr (age-adjusted)
• Teens (12+ years): Often adult sizing with caution

1. Select patient type - Adult, child, or infant.
2. Choose clinical indication - Why the catheter is needed.
3. Click "Calculate" to get colour coded starting size recommendation.
4. If you need to redo, click "Reset" to start fresh.

**All information is private, no data is saved or shared.**

This calculator helps suggest a typical starting catheter size based on common clinical guidelines.

The recommendation is based on standard sizing practices used in hospitals and general ward settings.

Please note: actual catheter choice must always consider the individual patient’s anatomy, history, and clinical condition. This tool is a guide, not a replacement for professional judgement.

Q1. What's the difference between a catheter and a foley?

• A "Foley" catheter is the standard urinary catheter with a balloon at the tip.
• After insertion, the balloon is inflated with sterile water (usually 10ml) to keep it from falling out.
• Other catheters (like straight catheters) don't have this balloon and are removed immediately after drainage.

Q2. What should you not do with a catheter?

• The catheter system is a direct highway for bacteria into your bladder.
• Lifting the drainage bag above your waist lets urine flow backward, bringing bacteria with it.
• Tugging can tear the delicate bladder lining.
• Ignoring leaks often means the catheter is blocked or too small - both need immediate attention to prevent kidney damage.

Q3. Why does French size matter more than length?

• French size (diameter) determines how much urine can flow per minute.
• A 14Fr drains about 30ml/minute, while 18Fr manages 50ml/minute.
• For retention patients, that extra 20ml/minute prevents dangerous bladder over-distension.
• Length matters less because 95% of adults fit standard sizes - it's like trouser waist size (varies) versus leg length (mostly standard).

Q4. Is a 14 French bigger than a 16 French?

• French size measures circumference (distance around the catheter).
• Since circumference = π × diameter, a higher French number means a wider catheter.
• It's confusing because it's not a direct diameter measurement, but the rule is simple: bigger number = bigger catheter.

Q5. What is the urine catheter size for male?

• Male urethras are longer and have natural narrow points (especially through the prostate).
• A 14-16Fr catheter usually passes comfortably through these areas while providing adequate drainage.
• For retention (blocked flow), we size up to 16-18Fr because the bladder muscle is stretched and produces more urine pressure needing faster drainage.

Q6. What is the urine catheter size for female?

• Female urethras are shorter and straighter than male, making catheterisation technically easier but leakage more common if size is wrong.
• A 12-14Fr catheter usually works well for routine drainage.
• Some women benefit from "female length" catheters (shorter) that reduce excess tubing but these aren't always available.

Q7. When should I size up for clots or bleeding?

• Blood contains clotting factors that turn liquid urine into solid obstructions within minutes.
• A 20Fr catheter has 36% more internal space than 16Fr - crucial for clot passage.
• For active bleeding, urologists use three-way catheters (22-24Fr) with an extra port to continuously flush the bladder with saline, preventing fatal clot retention.

Q8. What happens if catheter size is too big?

• A catheter that's too large can block the natural mucus and secretions that protect the urethra.
• This causes pressure ulcers inside the urine passage.
• The bladder then spasms painfully around this foreign object, and urine leaks around the sides because the main channel is blocked.
• This leaking urine carries skin bacteria into the bladder.

Q9. How often should catheters be changed?

• Catheters develop "biofilm" within 24 hours - a slimy bacterial layer that antibiotics cannot penetrate.
• However, changing catheters unnecessarily introduces new bacteria.
• The evidence-based approach is: "If it's working, not infected, and not causing discomfort - leave it alone."

Q10. When should a catheter be removed?

• The golden rule is "day 1 or day 3" - either remove immediately post-op (day 1) or wait until swelling reduces (day 3).
• Catheters should never become long-term solutions without specialist review. Each extra day increases infection risk by 5%.
• Bladder scans are performed to check urine volume before removal decisions.