Sand dollar
A sand dollar is a flat, burrowing sea urchin with a rigid, disc-shaped skeleton, often found in sandy coastal waters.
Also known as: sand dollar echinoid
How big is it?
8 cm · defined test diameter
Also 3.15 in
Defined test diameter · defined specimen
Typical recorded range: 5 cm to 10 cm.
A little perspective
Sand dollar vs Shuttlecock: length comparison
The overall length of a shuttlecock is about 1.06 times the test diameter of a sand dollar.
A sand dollar is a flat, burrowing sea urchin with a rigid, disc-shaped skeleton, often found in sandy coastal waters.
A shuttlecock is a feathered projectile used in badminton, designed to be struck by rackets.
Both rulers start at the same zero and share one linear scale. Artwork keeps its original proportions. Horizontal rulers compare the selected spans; vertical brackets also identify height on the artwork.
Measurements, assumptions & sources +
Sand dollar
Defined test diameter: 8 cm; defined specimen; range 5 cm–10 cm.
A defined living sand dollar with an 8 cm test diameter and 25 g mass. Species and maturity vary; short spines are included visually but do not define the rigid test span.
Smithsonian Ocean — Sea urchins and sand dollars
The marked defined test diameter is calibrated. Unmeasured illustration details are representative.
Shuttlecock
Overall length: 8.5 cm; representative; range 8 cm–9 cm.
A representative feather shuttlecock 85 mm long and 5 g, within international equipment tolerances. Synthetic skirts and speed grades differ.
Badminton World Federation — Statutes and equipment laws
The marked overall length is calibrated. Unmeasured illustration details are representative.
Use the visual comparison to explore its scale, then check the measurements and sources.
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Why this measurement?
Why we use 8 cm
We compare the test diameter of a sand dollar. This is an illustrative comparison value, not a claim that every example is the same. The recorded range is 5 cm to 10 cm.
A defined living sand dollar with an 8 cm test diameter and 25 g mass. Species and maturity vary; short spines are included visually but do not define the rigid test span.
The marked horizontal span follows the measured feature, not the edges of the image. How calibrated comparisons work →
Recorded properties
Dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 8 cm | 5 cm to 10 cm | defined specimen | |
| 25 g | 10 g to 50 g | defined specimen |
Around this scale
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Want to check the number?
The source records and measurement method remain available for inspection.
- Smithsonian Ocean — Sea urchins and sand dollarsSand-dollar identity, rigid test and living spine covering; the atlas uses a defined specimen.
There’s always another scale
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