One of the most common questions I hear in clinic is: "Doctor, will my stone pass on its own?" The honest answer depends almost entirely on the stone's size - but also its location, shape, and whether it is causing complications. This guide translates the evidence into a practical, size-by-size chart, explains when each of the three main treatments (RIRS, PCNL, ESWL) is appropriate, and tells you the warning signs that turn a kidney stone into an emergency.
The Kidney Stone Size Chart
The table below summarises pass rates and recommended treatment for each size category. These figures apply to ureteric stones - stones already in the ureter. Stones still sitting in the kidney are managed differently (they may be observed unless causing pain, infection, or growth).
| Stone Size | Spontaneous Pass Rate | Typical Symptoms | Recommended Treatment |
|---|---|---|---|
| ≤ 4 mm | 90–95% | Mild to moderate loin pain; blood in urine | Watchful waiting + high fluids + tamsulosin |
| 5–6 mm | 50–60% | Moderate renal colic; repeated episodes | Trial 4 weeks, then RIRS laser surgery if no passage |
| 7–9 mm | 20–25% | Severe colic; nausea; obstruction likely | RIRS (preferred) or ESWL if suitable |
| 10–14 mm | < 10% | Persistent obstruction; risk of kidney damage | RIRS for most; PCNL for large lower-pole stones |
| ≥ 15 mm | Rare / negligible | Chronic obstruction; staghorn stones possible | PCNL (first-line for stones ≥ 20 mm) |
Pass rates refer to spontaneous passage within 4 weeks in ureteric stones without surgical intervention. Source: European Association of Urology Guidelines on Urolithiasis 2024.
Watch: RIRS Laser Surgery for Kidney Stones Explained
RIRS vs PCNL vs ESWL: Which Is Right for Your Stone?
Three surgical treatments are available for kidney stones that cannot pass naturally. Understanding how they differ helps you ask the right questions in clinic.
RIRS (Retrograde Intrarenal Surgery)
A flexible ureteroscope - a thin, camera-tipped tube - is passed through the urethra, bladder and ureter into the kidney. No skin incision is required. A laser fibre pulverises the stone into fine dust that washes out in the urine. RIRS is the preferred treatment for stones of 7–20 mm, lower-pole stones, and patients who cannot stop blood-thinning medication. Stone-free rates are 85–95% for stones up to 15 mm. Hospital stay is typically one overnight. A DJ stent remains for 1–3 weeks post-procedure.
PCNL (Percutaneous Nephrolithotomy)
PCNL involves a small puncture (1 cm) in the back to pass a rigid scope directly into the kidney. It is the gold standard for stones larger than 20 mm, staghorn stones, and cases where a single-session clearance of a very large stone burden is required. Stone-free rates exceed 90% for stones of 20–40 mm. Hospital stay is 2–3 days. Mini-PCNL and Ultra-mini PCNL (punctures of 4–5 mm) now allow even large stones to be cleared with much less bleeding and a faster recovery than traditional PCNL.
ESWL (Extracorporeal Shock Wave Lithotripsy)
ESWL uses shock waves directed from outside the body to break stones into smaller fragments that the patient passes naturally. It requires no anaesthesia (or light sedation) and is truly non-invasive. However, it works best for stones of 5–10 mm in the upper ureter or kidney, soft calcium phosphate or uric acid stones, and patients who cannot undergo general anaesthesia. It is less effective for hard calcium oxalate monohydrate stones (very common in India), lower-pole kidney stones (fragments cannot drain easily against gravity), and stones larger than 15 mm. Multiple sessions may be needed.
| Factor | RIRS | PCNL | ESWL |
|---|---|---|---|
| Best stone size | 7–20 mm | > 20 mm | 5–10 mm |
| Skin incision | None | 1 cm | None |
| Anaesthesia | General/spinal | General/spinal | Sedation only |
| Hospital stay | 1 night | 2–3 nights | Day case |
| Stone-free rate (10–15 mm) | 85–92% | 90–95% | 55–70% |
| Safe on blood thinners | Yes | No | No |
Stone Composition: Why It Matters in India
In India, approximately 65–70% of kidney stones are calcium oxalate (either monohydrate or dihydrate). These are typically hard, dense, and white or brown on imaging. Monohydrate stones are particularly resistant to ESWL, making RIRS or PCNL the preferred options regardless of size.
- Calcium oxalate monohydrate (COM) - hardest; ESWL works poorly; RIRS or PCNL needed
- Calcium oxalate dihydrate (COD) - softer; responds better to ESWL; still easier to laser
- Uric acid stones - unique: can be dissolved medically by alkalinising urine (potassium citrate + high fluids); surgery only if dissolution fails
- Struvite / infection stones - form in the setting of chronic urinary infection; staghorn configuration common; PCNL + antibiotics required
- Cystine stones - rare; very hard; require PCNL or repeated RIRS; lifelong alkalinisation therapy to prevent recurrence
Stone composition is best determined by stone analysis after surgery - the removed fragments are sent to the lab and the result guides your stone prevention plan.
Fever + Kidney Stone = Emergency
Go to the emergency department immediately if you have a kidney stone AND any of:
- Temperature above 38°C (fever or chills)
- Rigors (uncontrollable shivering)
- Nausea and vomiting preventing oral medications
- Pain that is not controlled by paracetamol or diclofenac
- Decreased urine output or no urine for more than 8 hours
- Known single kidney or transplant kidney
Fever with an obstructing kidney stone means infected urine is backing up into the kidney - a condition called infected hydronephrosis or pyonephrosis. This can progress to gram-negative sepsis within hours. Emergency drainage (nephrostomy tube or DJ stent) is required before any definitive stone surgery can be performed. Never assume a fever alongside kidney stone pain is just a coincidence.
Unsure about your stone size or treatment options?
Dr. Nitin Shrivastava reviews your CT report and recommends the most appropriate, minimally invasive treatment - at Apollo Hospital Gurugram or Six Sigma Clinics Sector 50.
Book a ConsultationStone Prevention: Stop the Next Stone Before It Forms
The recurrence rate for kidney stones without intervention is 50% within 5 years and 70% within 10 years. Most stone formers benefit from a targeted prevention strategy based on their stone type, urine chemistry, and risk factors. A 24-hour urine metabolic workup identifies the specific abnormality (high oxalate, low citrate, high uric acid, high calcium) and allows targeted treatment - whether that is dietary modification, high fluid intake, potassium citrate, or thiazide diuretics.
The single most effective prevention strategy for all stone types is drinking enough water to produce at least 2.5 litres of urine per day. In Delhi NCR summers, this typically means drinking 3–4 litres of fluid per day. Pale straw-coloured urine throughout the day indicates adequate hydration.
Frequently Asked Questions
A 6 mm stone sits on the borderline. Clinical data shows that stones of 5–6 mm have roughly a 50–60% spontaneous passage rate, compared to over 90% for stones under 4 mm. Passage depends not just on size but on shape (smooth vs spiky), location (upper ureter stones take longer than lower ureter stones), and how narrow the ureter is at the ureterovesical junction. If there is no fever, the kidney is not obstructed on ultrasound, and pain is manageable with medication, a trial of medical expulsive therapy (tamsulosin 0.4 mg at night) for 4 weeks is reasonable. If the stone has not passed in 4 weeks, or pain becomes uncontrollable, RIRS laser surgery is the preferred next step.
As a practical rule: stones above 10 mm almost always require intervention. Stones of 7–9 mm will need surgery in roughly 75–80% of cases and watchful waiting risks prolonged obstruction. Stones of 5–6 mm can be observed for 4 weeks before deciding. Stones under 4 mm usually pass spontaneously. However, size is not the only criterion - fever with a stone is an emergency regardless of size (infected hydronephrosis can cause sepsis within hours and requires immediate nephrostomy or stent). Single-kidney patients, pregnant women, or patients with impaired kidney function require earlier surgical intervention for any stone causing obstruction.
The procedure itself is performed under general or spinal anaesthesia - you will feel nothing during surgery. Afterwards, most patients experience mild burning during urination and pink-coloured urine for 2–4 days. A ureteral stent (DJ stent) is placed at the end of the procedure and remains for 1–3 weeks; this can cause a dull ache in the flank, frequent urination, and occasionally blood-tinged urine. The stent is removed as a brief outpatient procedure. Overall, patients rate RIRS post-operative discomfort as mild to moderate - far less than passing a stone naturally through the ureter.
Renal colic - the severe, wave-like pain of a stone moving through the ureter - typically lasts 20–60 minutes per episode but can recur over several days or weeks until the stone passes. Once a stone reaches the bladder, pain usually disappears almost immediately. If a stone is stuck in the upper ureter causing obstruction, a constant dull loin ache can persist for days or weeks, gradually damaging the kidney if untreated. If pain has lasted more than 72 hours without any passage, or if you develop fever, chills, or vomiting with the pain, seek medical review urgently rather than waiting for the pain to resolve.
In India, the majority of kidney stones (approximately 65–70%) are calcium oxalate stones. The main dietary contributors are: (1) Very high oxalate foods - spinach (palak), tomatoes, nuts, chocolate, and tea - particularly when eaten with low-calcium diets, which paradoxically increases oxalate absorption; (2) Excess animal protein - purines from meat and poultry raise uric acid and lower urine pH, favouring both calcium oxalate and uric acid stones; (3) Very high sodium intake - excess salt raises urinary calcium; (4) Inadequate fluid intake - the most important factor, especially in Delhi NCR summers, where dehydration is common. Contrary to popular belief, most patients with calcium oxalate stones should NOT restrict dietary calcium - low-calcium diets increase stone risk.