In vivo
Tumour volume from calipers
Compute tumour volume from caliper measurements, plot a growth curve per animal and estimate the doubling time.
Per line: animal id (optional), day (optional), then the dimensions. How many dimensions are needed follows from the formula you chose. Commas, tabs or spaces all work as separators.
Summary by animal
Length × width² ÷ 2 is the usual estimate for subcutaneous models and assumes an ellipsoid whose two smaller diameters are equal; always enter the larger diameter as the length. Doubling time comes from a linear fit of log volume against day and is not computed below three points. Set the volume limit from your own approved protocol — this tool suggests no threshold.
Formula
V = length × width² ÷ 2
- length
- the largest diameter measured
- width
- the diameter perpendicular to it
- ÷ 2
- comes from simplifying the ellipsoid volume, assuming the two smaller diameters are equal
- doubling time
- log 2 divided by the slope of log volume against day
Worked example
A tumour measuring 12 by 8 millimetres
- length = 12 mm
- width = 8 mm
- Square the width: 8 squared is 64.
- Multiply by the length: 12 times 64 is 768.
- Divide by two.
Answer 384 cubic millimetres
Common mistakes
- Entering length and width the wrong way round. Because the width is squared, swapping them changes the answer badly: the same tumour would read 576 instead of 384.
- Changing formula midway through a study. Volumes from different formulas are not comparable; pick one at the start and keep it, including in the methods section.
- Measuring an ulcerated or necrotic tumour with calipers. The number no longer reflects living mass, and in most protocols ulceration is itself an endpoint.
- Computing a doubling time from two points. Tumour growth is noisy; this tool declines below three points.
Frequently asked
Which formula is more accurate?
Length times width squared over two is the usual choice for subcutaneous models and correlates well with excised tumour mass. The full ellipsoid is worth it only if you genuinely measure the height rather than guessing it.
What volume threshold should I use as an endpoint?
This tool deliberately proposes none. The threshold must come from your approved ethics protocol; the limit field exists so you can enter your own number and have measurements above it flagged.
How should I record a volume of zero?
Do not enter zero dimensions for impalpable tumours, since they break the logarithmic doubling-time fit. Leave that day out and note it in your own records.