How to read this calculator
Enter all three dimensions of one scan, or of both, in cm or mm; the unit applies to both scans. The bladder scan alone gives the bladder volume, and the post-void scan alone gives the post-void residual (PVR). With both scans, the first is shown as the pre-void volume. A scan with only one or two dimensions is not calculated.
How the volume is calculated
Bladder estimate (0.52): 0.52 × length × width × depth.
In 85 patients undergoing urodynamics, 0.52 was the only one of four tested coefficients without a statistically significant difference from catheter volume (Araklitis 2019). The accessible abstract does not specify the ultrasound route or dimensional measurement protocol; applicability to other settings is uncertain.
The coefficient 0.52 is a rounded approximation to π/6 and gives 0.69% less for the same three diameters. Published empirical coefficients differ by population, shape and measurement method; they are not interchangeable corrections.
A 220-patient CT study in patients without reportable bladder disease reported a mean estimate of 121.0 mL using 0.52 × three diameters, compared with 128.5 mL by 3D Slicer, with larger errors in small bladders (Shen 2025). Only its abstract was available; its dimensional acquisition protocol and size-group cutoffs have not been verified.
How to measure
For ultrasound, measure the maximum width on a transverse image, then the maximum craniocaudal length and AP depth on a longitudinal (sagittal) image, from inner wall to inner wall. The order of the three numbers does not change the volume.
Scan as soon as possible after the patient voids (ICS teaching module 2016).
The ACR abdominal ultrasound practice parameter says a post-void residual may be quantified and reported; it sets no volume threshold.
The AIUM/IUGA urogynecological ultrasound practice parameter (2019) describes a separate perineal two-diameter method, not this transabdominal three-diameter estimate.
Post-void residual
Published PVR reference values depend on population, method and timing. The ICS teaching module gives expert-opinion examples of less than 30 mL as insignificant and persistently greater than 50 mL as potentially important. The IUGA/ICS female terminology report describes study-based upper limits of 30 mL with immediate ultrasound and 50 or 100 mL with delayed catheter measurements, and requires confirmation of an isolated raised value. EAU 2026 and the held AUA 2021 initial-evaluation text do not provide a universally applicable significant-PVR cutoff. This calculator therefore reports estimates without a normal/abnormal classification.
For men with chronic urinary retention (residual volume greater than 1 litre or a palpable or percussable bladder), NICE CG97 recommends serum creatinine testing and imaging of the upper urinary tract.
Accuracy
Three-diameter estimates depend on bladder shape and measurement technique. Hakenberg's 1983 abstract reports an average error of ±25% between 100 and 500 mL and frequent false-negative readings below 50 mL in that study. Its full protocol was not available, and this is not a universal accuracy bound or a validated 50 mL reliability cutoff for this calculator. Other studies have reported different performance, including accurate small-volume assessment in a paediatric 0.52 study. Irregular contours and neurogenic or surgically altered bladders require particular caution when interpreting a geometric estimate. Differences between two scan estimates also include measurement error and any filling between scans.
Children
Paediatric studies have used different coefficients and age-specific methods. A 0.52 study in 101 children reported good correlation but underestimation at large volumes; other studies, including neurogenic-bladder cohorts, found substantial disagreement. This calculator does not estimate expected capacity or classify paediatric PVR. Fetal bladder assessment is outside its reviewed scope.
In children undergoing uroflowmetry, EAU uses ([age in years] + 1) × 30 mL as an age-expected capacity benchmark and states that the voided volume should be at least 50% of that capacity. This is not a normal range for a single ultrasound bladder estimate. In its paediatric UTI guidance, EAU advises before- and after-voiding ultrasound in toilet-trained children.
Worked example
Ma 2025 reports bladder dimensions at age 5 of 9.0 × 5.5 × 6.4 cm when filled and 4.1 × 2.2 × 3.0 cm after urination. Using 0.52 gives 164.736 mL and 14.0712 mL, displayed as 164.74 mL and 14.07 mL. The authors report about 165 mL and 14 mL. The triplet axes are not specified, and these author-reported estimates are not an independent measurement of true bladder volume.
| Item | Value |
|---|---|
| Bladder scan (pre-void if paired): Dimension 1 | 9 cm |
| Bladder scan (pre-void if paired): Dimension 2 | 5.5 cm |
| Bladder scan (pre-void if paired): Dimension 3 | 6.4 cm |
| Post-void scan (optional): Dimension 1 | 4.1 cm |
| Post-void scan (optional): Dimension 2 | 2.2 cm |
| Post-void scan (optional): Dimension 3 | 3 cm |
| Pre-void volume | 164.74 mL |
| Post-void residual (PVR) | 14.07 mL |
No PVR cutoff applies universally. These estimates are approximate; see Accuracy.
Frequently asked questions
What is a normal post-void residual volume?
There is no universal cutoff for this calculator; published reference values depend on population, method and timing. See Post-void residual for the guideline context.
How do you calculate bladder volume on ultrasound?
Enter three internal dimensions; this tool uses 0.52 × length × width × depth. See How to measure for the ultrasound views.
What is the bladder volume formula (0.52 or 0.7)?
This calculator uses 0.52. Published empirical coefficients depend on the study method and population; see How the volume is calculated.
How soon after voiding should the post-void residual be measured?
As soon as possible after voiding; see How to measure for the timing limitations.
Can bladder volume be measured on CT?
CT dimensions can be entered for an approximate geometric estimate. See How the volume is calculated for the CT evidence and its limitations.
References
- ACR–AIUM–SPR–SRU Practice Parameter for the Performance of an Ultrasound Examination of the Abdomen and/or Retroperitoneum, revised 2026 (Resolution 10), §V.I. https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards
- Asimakopoulos AD, De Nunzio C, Kocjancic E, Tubaro A, Rosier PF, Finazzi-Agrò E. Measurement of post-void residual urine (ICS teaching module). Neurourol Urodyn. 2016;35(1):55-57. doi:10.1002/nau.22671. PMID 25251215.
- EAU Guidelines on Non-neurogenic Female LUTS, 2026 edition, §3.5 Post-void residual volume. https://uroweb.org/guidelines/non-neurogenic-female-luts/chapter/diagnosis
- EAU Guidelines on the Management of Non-neurogenic Male LUTS, 2026 edition, §4.8 Post-void residual urine. https://uroweb.org/guidelines/management-of-non-neurogenic-male-luts/chapter/diagnostic-evaluation
- EAU Guidelines on Paediatric Urology, 2026 edition, §13.2.3 (daytime lower urinary tract conditions) and §12.5.1 (urinary tract infections in children). https://uroweb.org/guidelines/paediatric-urology
- Haylen BT, de Ridder D, Freeman RM, et al. An International Urogynecological Association (IUGA)/International Continence Society (ICS) joint report on the terminology for female pelvic floor dysfunction. Neurourol Urodyn. 2010;29(1):4-20. doi:10.1002/nau.20798. (Postvoid residual, p. 11.)
- Lerner LB, McVary KT, Barry MJ, et al. Management of lower urinary tract symptoms attributed to benign prostatic hyperplasia: AUA guideline part I, initial work-up and medical management. J Urol. 2021;206(4):806-817. doi:10.1097/JU.0000000000002183. (Initial Evaluation.)
- NICE. Lower urinary tract symptoms in men: management. Clinical guideline CG97, recommendation 1.7.4. https://www.nice.org.uk/guidance/cg97/chapter/Recommendations
- AIUM/IUGA Practice Parameter for the Performance of Urogynecological Ultrasound Examinations. J Ultrasound Med. 2019;38(4):851-864. doi:10.1002/jum.14953.
- Taus PJ, Manivannan S, Dancel R. Bedside assessment of the kidneys and bladder using point of care ultrasound. POCUS J. 2022;7(Kidney):94-104. doi:10.24908/pocus.v7iKidney.15347. PMID 36896106.
- Araklitis G, et al. Can we replace the catheter when evaluating urinary residuals? Neurourol Urodyn. 2019;38(4):1100-1105. doi:10.1002/nau.23963. PMID 30843290. Abstract reviewed.
- Shen J, Zuo Y, Song J, et al. Impact of bladder size and shape on the accuracy of formula method for bladder volume evaluation. Int Urol Nephrol. 2025;57(2):333-339. doi:10.1007/s11255-024-04211-5. PMID 39312017. Abstract reviewed.
- Hakenberg OW, Ryall RL, Langlois SL, Marshall VR. The estimation of bladder volume by sonocystography. J Urol. 1983;130(2):249-251. doi:10.1016/s0022-5347(17)51087-3. PMID 6876269. Abstract reviewed.
- Erasmie U, Lidefelt KJ. Accuracy of ultrasonic assessment of residual urine in children. Pediatr Radiol. 1989;19(6-7):388-390. doi:10.1007/BF02387634. PMID 2671896. Abstract reviewed.
- Tessi C, Burek CM, Sager C, et al. Bladder volume assessment in pediatric patients with neurogenic bladder: is ultrasound an accurate method? Urology. 2021;147:250-255. doi:10.1016/j.urology.2020.10.005. PMID 33053401. Abstract reviewed.
- Ma L, Zhang Y, Yao S, He S, Li J. Sensory integration combined with interoceptive interventions for functional urinary incontinence in children: a case report. Front Rehabil Sci. 2025;6:1599599. doi:10.3389/fresc.2025.1599599. PMID 40697955. (Worked example: Case presentation.)