Enter the test tube inner radius and the height of the straight cylindrical section (choose units) into the Test Tube Volume Calculator. This calculator uses the right circular cylinder volume model (flat-bottom / cylindrical approximation) and will evaluate and display the Test Tube Volume.

Test Tube Volume Calculator

Enter exactly 2 values to calculate the missing variable.

Note: Uses the cylindrical volume model (flat-bottom/straight-sided approximation).

Test Tube Volume Formula

This calculator estimates the volume of a test tube by treating it as a right circular cylinder. For the most accurate result, use the inside radius of the tube and the inside height or liquid height, depending on whether you want total capacity or the amount currently inside.

V = \pi r^2 h
Variable Meaning
V Test tube volume
r Inside radius of the test tube
h Height of the tube or height of the liquid column

If the measurements are entered in centimeters, the result is in cubic centimeters. If they are entered in inches, the result is in cubic inches. Always keep both measurements in the same unit before calculating.

How to Calculate Test Tube Volume

  1. Measure the inside radius of the tube.
  2. Measure the internal height of the tube, or the liquid height if the tube is only partially filled.
  3. Square the radius.
  4. Multiply by pi.
  5. Multiply by the height to get the volume.

If you know the diameter instead of the radius, convert it first:

r = \frac{d}{2}

Then use the main volume equation.

Example

Suppose a test tube has an inside diameter of 1.5 cm and a liquid height of 12 cm.

r = \frac{1.5}{2} = 0.75 \text{ cm}
V = \pi (0.75)^2 (12) \approx 21.21 \text{ cm}^3
21.21 \text{ cm}^3 = 21.21 \text{ mL}

So the tube contains about 21.21 mL of liquid at that fill height.

Capacity vs. Liquid Volume

The same equation can be used for two different purposes:

  • Total capacity: use the full internal height of the test tube.
  • Current liquid volume: use only the height of the liquid inside the tube.

This distinction matters in lab work, manufacturing, storage, and dosing applications where the usable fill level may be less than the full tube height.

Measurement Tips

  • Use internal dimensions, not external dimensions.
  • Make sure radius and height use the same unit system.
  • Small radius errors can create large volume errors because the radius is squared in the formula.
  • For narrow tubes, a caliper usually gives a better diameter measurement than a ruler.
  • If you measure diameter, divide it by two before entering the value as radius.

Rounded-Bottom Test Tubes

Some real test tubes have a rounded bottom instead of a perfectly flat cylindrical end. In that case, the simple cylindrical formula gives an approximation. If the tube has a hemispherical bottom with the same radius as the tube body, a more detailed model is:

V = \pi r^2 h + \frac{2}{3}\pi r^3

Use this version only when the straight-side height is measured separately from the rounded base. For quick estimates, the standard cylindrical formula is usually sufficient.

Common Conversions

1 \text{ cm}^3 = 1 \text{ mL}
1000 \text{ cm}^3 = 1 \text{ L}
1 \text{ in}^3 \approx 16.387 \text{ mL}

Common Questions

Should I enter diameter or radius?
Enter the radius. If you only have the diameter, divide it by two first.

What happens if I mix units?
Convert the measurements so they match before calculating. Otherwise, the result will be incorrect.

Why does the result change so much when radius changes a little?
Because the cross-sectional area depends on the square of the radius, even a small change in radius has a strong effect on volume.

Can this formula be used for partially filled tubes?
Yes. Use the liquid height instead of the full internal height to estimate the amount of liquid currently in the tube.