Snapping Turtle Age by Size Chart (Common and Alligator)

You can estimate the age of a snapping turtle by its shell length until it reaches maturity. This guide shows growth rates for common and alligator snapping turtles, plus quick charts, weight by age, and answers to the most asked questions.

How to measure for the charts

Measure the carapace straight across from the front notch to the back edge. Do not follow the curve of the shell. Write the length in inches or centimeters and use the charts below for an age range. Diet, temperature, sex, and habitat all affect growth, so treat this as an estimate.

Snapping Turtle Growth Rate Chart

Two snapping turtle hatchlings on a hand — Hatchlings grow fast in the first years

Short answer. Snapping turtles grow quickly until they mature. After that growth slows a lot, so size is most useful for estimating age in the first ten years.

You can read a detailed study of growth rates for common snapping turtles in Texas in this research article by Thanchira Suriyamongkol. The big picture is the same across many regions. Fast early growth then a long slow climb.

Use the species charts below to get a practical age range from shell length. Then confirm with weight and overall condition.

Common Snapping Turtle Age by Size

Short answer. From hatchling to ten years, common snappers go from about 1.1 inches to around 10 inches in shell length. After that size increases slowly.

Hatchlings are about 1.1 inches, or 2.9 centimeters. By one year they reach about 3.5 to 5 inches. At two to three years most measure 5.3 to 6.1 inches. By four to six years many fall between 4.7 and 9.4 inches. At ten years the shell is close to 10 inches. Growth after maturity continues, just at a slower pace.

Age	Carapace length
0	1.1 in (2.9 cm)
1	3.5 to 5 in (8.9 to 12.7 cm)
2 to 3	5.3 to 6.1 in (13.5 to 15.5 cm)
4 to 6	4.7 to 9.4 in (11.9 to 23.9 cm)
10	about 10 in (25.4 cm)
15 to 40	14 to 18.5 in (35.6 to 47 cm)

Mature common snapping turtle resting on a bank — A mature common snapping turtle

By ten years many common snappers are mature. Expect only small size gains after this point.

Alligator Snapping Turtle Age by Size

Short answer. Alligator snappers track common snappers in the first decade, then they keep adding length for much longer. Adults can reach well over 20 inches.

Alligator snapping turtle near a pond — Give alligator snappers lots of room

Hatchlings measure about 1.5 inches. By one year they are around 2.5 to 4 inches. At two years many reach 5 to 6 inches. By three years they often measure 6 to 8 inches. Around five years they reach 8 to 10 inches. By ten years most are 10 to 12 inches. From ten to twenty years the average climbs to 12 to 16 inches. From forty years onward some exceed 26 inches.

Carapace Length by Age

Age	Carapace length
0	1.5 in (3.8 cm)
1	2.5 to 4 in (6.35 to 10.2 cm)
2	5 to 6 in (12.7 to 15.2 cm)
3	6 to 8 in (15.2 to 20.3 cm)
5	8 to 10 in (20.3 to 25.4 cm)
10	10 to 12 in (25.4 to 30.5 cm)
10 to 20	12 to 16 in (30.5 to 40.6 cm)
40 to 50+	16 to 26+ in (40.6 to 66+ cm)

Weight by Age

Alligator snapping turtle swimming in clear water — Weight supports your length estimate

You can also estimate age from weight if you can weigh the turtle safely.

Age	Mass or weight
1	1 to 2 lb (0.4 to 0.9 kg)
10	10 to 35 lb (4.5 to 15.9 kg)
10 to 20	about 35 lb (15.9 kg)
40	about 46 lb (20.9 kg)
50+	males 64 to 176 lb (29 to 80 kg). females about 46 lb

Looking for all snapping turtle types in one place? See five types of snapping turtles when you are done here.

Frequently Asked Questions

How big is a 100 year old snapping turtle

Very large. Snapping turtles keep adding size through life, just much slower after maturity. One famous common snapper named Big Snap Daddy weighs about 90 lb at 93 years. The largest alligator snapper on record was estimated near 100 years and weighed about 249 lb.

How old is a 1 foot snapping turtle

A shell length near 12 inches often points to around 10 to 12 years in both common and alligator snappers. Always confirm with species and weight.

How old is a full grown snapping turtle

Males of the common species often mature around 4 to 6 years at roughly 18 to 19 cm shell length. Females mature closer to 10 to 12 years at 20 to 22 cm. Growth does continue after maturity, only much slower. Alligator snappers mature later and can reach larger sizes.

Not sure how to identify a snapping turtle? Open our quick guide in a new tab: how to identify a snapping turtle.

Conclusion

Size is a handy age clue in the first decade. Measure the shell straight across, look up the length in the chart, and cross check with weight and species. After maturity the changes are slow, so treat any number as a range, not an exact birthday.