What is the expected bladder capacity by age for children?

With the ICCS formula (age + 1) × 30 mL, expected capacity is 60 mL at 1 year, 150 mL at 4, 210 mL at 6, 270 mL at 8, 330 mL at 10 and 390 mL at 12, after which adult capacity is approached. Each year adds 30 mL.

What is the Koff formula for bladder capacity?

Koff (1983) estimated capacity in ounces as age in years + 2, which is (age + 2) × 30 mL. It gives 30 mL more than the ICCS formula at every age, for example 210 mL instead of 180 mL at 5 years. It came from cystometry in 35 anesthetized children.

What is the Kaefer formula?

Kaefer et al. (1997) proposed a two-part formula: capacity (oz) = 2 × age + 2 for children under 2 years and age ÷ 2 + 6 for children 2 years and older. It flattens with age, giving 270 mL at 6 years and 360 mL at 12 years.

How do you estimate bladder capacity in an infant?

A commonly used infant formula is Holmdahl's 38 + 2.5 × age in months (mL), so about 53 mL at 6 months. The ICCS (age + 1) × 30 formula is intended for older children.

What maximum voided volume is considered small or large?

The ICCS 2016 terminology update calls a maximum voided volume, excluding the first morning void, small if it is below 65 % of expected bladder capacity and large if it is above 150 %. It states that EBC is applicable for children aged 4 to 12 years.

What post-void residual is abnormal in a child?

The ICCS update gives these upper limits: at 4–6 years a single PVR above 30 mL or above 21 % of bladder capacity (voided volume + PVR), or repeated PVR above 20 mL or 10 %; at 7–12 years a single PVR above 20 mL or 15 %, or repeated above 10 mL or 6 %. The bladder should be neither under-filled ( 115 % EBC) and PVR measured within 5 minutes of voiding.

What is nocturnal polyuria in a child with bedwetting?

ICCS defines nocturnal polyuria in children with enuresis as nocturnal urine output (night diaper weight gain plus the first morning void) above 130 % of expected bladder capacity for age, for example above 273 mL for a 6 year old (210 mL EBC).

Does this calculator estimate adult bladder capacity?

No. The pediatric formulas level off around 12 years (390 mL by ICCS). Adult capacity is assessed from a voiding diary or urodynamics, not an age formula.

Is this tool a substitute for clinical evaluation?

No. Formulas give reference values only, and individual children vary. Clinical assessment, a voiding diary, ultrasound and, where needed, urodynamics are required for diagnosis or treatment decisions.

Bladder Capacity Calculator

Estimate a child's expected bladder capacity with the ICCS (age + 1) × 30 mL, Koff (age + 2) × 30 mL, Kaefer or infant Holmdahl formula, and compare a diary maximum voided volume, nocturnal urine volume or post-void residual with ICCS thresholds.

Expected bladder capacity in children is usually estimated as (age + 1) × 30 mL (ICCS) or (age + 2) × 30 mL (Koff): about 180 or 210 mL at age 5 and 390 or 420 mL at age 12.

Patient details

Age

ICCS states its formula applies from 4 to 12 years; use months for infants.

Maximum voided volume (optional)

Largest daytime void in the diary, excluding the first morning void.

Nocturnal volume and post-void residual (optional, mL)

Nocturnal urine volume

Night diaper weight gain (1 g ≈ 1 mL) plus the first morning void.

Voided volume

Residual (PVR)

PVR measured by ultrasound within 5 minutes of the same void.

Enter an age, then click Calculate.

Expected bladder capacity by age: formula comparison (mL)

Age	ICCS (age + 1) × 30	Koff (age + 2) × 30	Kaefer	ICCS small / large MVV
1 year	60	90	120	< 39 / > 90
2 years	90	120	210	< 59 / > 135
3 years	120	150	225	< 78 / > 180
4 years	150	180	240	< 98 / > 225
5 years	180	210	255	< 117 / > 270
6 years	210	240	270	< 137 / > 315
7 years	240	270	285	< 156 / > 360
8 years	270	300	300	< 176 / > 405
9 years	300	330	315	< 195 / > 450
10 years	330	360	330	< 215 / > 495
11 years	360	390	345	< 234 / > 540
12 years	390	420	360	< 254 / > 585

Koff and Kaefer were published in ounces; 1 oz is taken as 30 mL, as in clinical use. Kaefer: (2 × age + 2) oz under 2 years, (age ÷ 2 + 6) oz from 2 years. Infants: Holmdahl 38 + 2.5 × months mL. Small/large MVV limits are 65 % and 150 % of the ICCS value.

ICCS thresholds, scope and sources

Maximum voided volume (first morning void excluded): small < 65 % EBC, large > 150 % EBC; EBC applies to ages 4–12.
Nocturnal polyuria (children with enuresis): nocturnal urine output > 130 % EBC.
Post-void residual, bladder capacity = voided volume + PVR: ages 4–6 elevated if a single PVR > 30 mL or > 21 % of capacity; ages 7–12 if > 20 mL or > 15 %. Repeated measurements use the lower limits 20 mL / 10 % and 10 mL / 6 %. Valid when the bladder was filled to 50–115 % of EBC.

This is not an ultrasound bladder-volume calculator, an adult-capacity prediction or a diagnosis. Values stay in this browser and are not submitted or stored.

Sources: ICCS terminology update (Austin et al., 2016), Koff, Urology 1983, Cambridge University Hospitals pediatric bladder diary.

Quick answer

Expected bladder capacity in children is usually estimated as (age + 1) × 30 mL (ICCS) or (age + 2) × 30 mL (Koff): about 180 or 210 mL at age 5 and 390 or 420 mL at age 12. ICCS calls a maximum voided volume below 65 % of the estimate small and above 150 % large.

Examples

Age	ICCS (age + 1) × 30	Koff (age + 2) × 30
2 years	90 mL	120 mL
4 years	150 mL	180 mL
6 years	210 mL	240 mL
8 years	270 mL	300 mL
10 years	330 mL	360 mL
12 years	390 mL	420 mL

Enter the child's age, and optionally a diary volume, nocturnal volume or residual, to compare them with ICCS thresholds.

Summary

This pediatric reference tool computes expected bladder capacity (EBC) with the ICCS equation (age + 1) × 30 mL, and shows the Koff (age + 2) × 30 mL, Kaefer and infant Holmdahl estimates for comparison. A diary maximum voided volume is placed against the ICCS small (< 65 %) and large (> 150 %) limits, nocturnal urine volume against the 130 % nocturnal-polyuria limit, and a post-void residual against the ICCS age-specific limits. Expected capacity, maximum voided volume, residual and cystometric capacity are different measurements.

How it works

Enter the child's age in completed years (1–12), or in months for an infant under 1 year.
The calculator shows the ICCS expected bladder capacity (EBC = (age + 1) × 30 mL) and the Koff, Kaefer and, for infants, Holmdahl estimates side by side.
Optionally enter the maximum daytime voided volume from a diary: it is shown as a percentage of EBC, where ICCS calls < 65 % small and > 150 % large.
Optionally enter the nocturnal urine volume (night diaper weight plus first morning void): ICCS defines nocturnal polyuria in enuresis as > 130 % of EBC.
Optionally enter a post-void residual and the voided volume of the same void: bladder capacity = voided volume + PVR, compared with the ICCS age-specific limits.

Use cases

Clinicians and nurses reviewing a pediatric frequency-volume chart against age-expected capacity.
Checking whether a measured residual after voiding exceeds the ICCS limit for a 4–6 or 7–12 year old.
Screening nocturnal urine volume in a child with bedwetting for nocturnal polyuria.
Comparing the Koff and ICCS formulas that different textbooks and calculators use.
Urology and pediatrics students learning the expected-capacity equations.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu