Egg Generator

About the Egg Generator

This app makes 3D-printable models of real eggs, at life size. Pick a species (birds, and now turtles too) to load its egg, or change the four parameters to make any other egg. You can type values outside a slider’s range into its number box.

Where the eggs come from. Each species’ length and width are averages of measured eggs from published sources: field guides, museum catalogues, handbooks such as Bent’s Life Histories of North American Birds and Schönwetter’s Handbuch der Oologie, and journal papers. The line under the species name says where the size comes from, and links to the egg’s page in the egg compendium, which lists every source. For some eggs we haven’t found measurements yet; their size is estimated from related species and the page says so. The end roundness and diameter location (the egg’s taper) are estimated from typical eggs of the same group, so they are less certain than the length and width.

Making your egg. Generate 3D model makes an STL file in millimetres, at life size, ready for any slicer. The volume and mass are worked out from the same shape (the density is about that of a fresh egg; change it for other materials). Print a stand for this egg opens the Savi Made Stand Generator with a round stand sized to hold the egg upright.

Using your eggs. You can use the egg models you make here however you like, including commercially: print them, paint them, display them, share them, and make and sell them. Unlike the 3D models in the Savi Made shop, they aren't limited to personal use. The one thing I ask is credit. Whenever you show or sell the eggs publicly (prints on display, product listings, photos, videos, social media posts or written work), include:

“Egg geometry created with the Savi Made Egg Generator (savimade.ca)”

Make savimade.ca a live link where the platform allows. On social media you can instead tag Savi Made (Instagram @savi_made, Facebook @SaviMade, TikTok @savimade) and mention Savi Made in the caption. See also the attribution section of the Terms and Conditions.

Payments and your file. The Egg Generator runs separately from the Savi Made shop. Payments go straight through Stripe, so they won't appear in your shop account or order history, even when you're signed in. Your egg file is made in your own browser and isn't stored anywhere, not on this site and not in your account, so save it to your device right after paying. Stripe emails you a receipt; if a download goes wrong or you lose the file, get in touch with your receipt and I'll sort it out.

The egg-shape formula

Every egg outline here comes from the egg-shape formula published by F. W. Preston in 1953, which he called the “standard avian egg-shape”. It is still regarded as one of the most accurate descriptions of the shape of birds’ eggs (Biggins et al. 2022). It uses four numbers:

• Length (L): the egg from end to end, in mm.
• Width (B): the egg across its widest part, in mm.
• End roundness (D): how blunt or pointed the two ends are. Half the length gives a plain oval; a smaller number makes both ends more pointed, and a larger one makes them blunter, up to a capsule shape at the full length.
• Diameter location (n): how much bigger one end is than the other. At 0 both ends are the same; higher numbers move the widest part towards the blunt end and taper the other end more. Most bird eggs are between about 0.5 and 3.

The outline is the egg’s radius r (half its width) at each point along its length:

r(t) = s · ^B⁄₂ · √1 − t² · (1 + c₁ t + c₂ t²)

• t is the position along the egg, from −1 at the pointed end to +1 at the blunt end (t = 2x / L, where x is the distance from the middle in mm).
• c₁ = n / 10 is Preston’s asymmetry term: it makes one end bigger than the other.
• c₂ = D / L − ½ is his “biconical” term: it blunts or sharpens both ends equally.
• s scales the outline so that the widest part is exactly B.

With c₁ and c₂ both 0 the formula is a plain ellipse. The 3D egg is this outline spun around the egg’s long axis, and its volume is V = π∫r² dx, added up along the length.

Preston, F. W. (1953). The shapes of birds’ eggs. The Auk 70: 160–182.
Biggins, J. D., Montgomerie, R., Thompson, J. E. & Birkhead, T. R. (2022). Preston’s universal formula for avian egg shape. Ornithology 139(4): ukac028.

© 2026 Lincoln Savi, Savi Made. The Egg Generator and its species data are the work of Savi Made; its egg outlines use F. W. Preston’s egg-shape formula (1953).

Know the parameters for another species, or think an egg is wrong? Let me know.