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 across
Also 3.15 in
Defined test diameter · defined specimen
Typical recorded range: 5 cm to 10 cm.
A little perspective
About the same scale as Shuttlecock.
Shuttlecock: A shuttlecock is a feathered projectile used in badminton, designed to be struck by rackets.
Measurements, assumptions & sources +
Sand dollar
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
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.
Change your perspective
Put it next to…
Choose a suggestion to redraw the comparison, or open its page to learn what it is.
Why this measurement?
Why we use 8 cm
For comparison, this page uses defined test diameter. This is labelled defined specimen: an explicit comparison model rather than a claim that every example has the same value. 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 named feature; transparent margins and unmeasured details do not alter it. How calibrated comparisons work →
Recorded properties
Sand dollar 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
Go smaller. Go bigger.
These links use compatible length records, ordered around the selected value.
Nearest lower value · Living thingsAntarctic krill6 cmAntarctic krill (Euphausia superba) are small, shrimp-like marine crustaceans that serve as a vital food source for many Antarctic animals.
Around the same scale · Living thingsHummingbird8 cmThe hummingbird is a tiny bird capable of hovering in mid-air by rapidly flapping its wings to feed on nectar.
Nearest higher value · Living thingsMouse9 cmA mouse is a small rodent with a pointed snout and a long, thin tail.Sources and method
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
Follow your curiosity.
SportShuttlecock8.5 cmA shuttlecock is a feathered projectile used in badminton, designed to be struck by rackets.
Everyday thingsPeach7 cmA peach is a juicy fruit with fuzzy skin and a central stone, grown on the tree Prunus persica.
Living thingsNudibranch10 cmA nudibranch is a soft-bodied marine mollusc, often brightly coloured, commonly known as a sea slug.
PeopleIndex finger8 cmThe index finger is the second finger of the human hand, located between the thumb and the middle finger.
Living thingsMantis shrimp10 cmA mantis shrimp is a marine crustacean that hunts using specialised limbs to strike or spear prey.
Everyday thingsPomegranate10 cmA pomegranate is a round fruit from the Punica granatum tree, containing many edible seeds surrounded by juicy pulp.
SportLacrosse ball6.35 cmA lacrosse ball is a solid rubber ball used in the sport of lacrosse, designed to meet official standards for play.
ContainersEspresso demitasse60 mlAn espresso demitasse is a small porcelain cup used for serving concentrated espresso coffee.