Researched and devised by Dr. Oliphant Jackson, the Jackson ratio is a method of determining whether a member of the tortoise species Testudo graeca or Testudo hermanni is maintaining its optimum bodyweight, which is necessary for a successful hibernation.^[1]

The Jackson ratio is calculated by taking the weight of the tortoise in grams and dividing it by the cube of the length of the tortoise's carapace in centimeters.^[1] This is essentially a value of the density of the tortoise in g/cm³. The optimal value for this ratio is 0.21 with a range of 0.18–0.22 being acceptable for hibernation. Values significantly less than this indicate an underweight tortoise and larger values are indicative of overweight tortoises.

The Jackson ratio is expressed as a graph of minimum and optimum weights for a given carapace length. This exhibits the same principle without the maths.

• ULf Edqvist. "Tortoise Trust Web - The Jackson Ratio Graph - Inappropriate Use". Tortoisetrust.org. Retrieved 2017-02-24.
• A. C. Highfield. "Tortoise Trust Web - How to Measure your Tortoise". Tortoisetrust.org. Retrieved 2017-02-24.
• "Heosemys grandis forum - Jackson ratio". Heosemys.org. Retrieved 2017-02-24.

v t e Tortoise family
Kingdom: Animalia Phylum: Chordata Class: Reptilia Subclass: Anapsida Order: Testudines Suborder: Cryptodira Superfamily: Testudinoidea Family: Testudinidae
Genera	Species of the tortoise family
Agrionemys	Russian tortoise
Aldabrachelys	Aldabra giant tortoise (subspecies: A. g. arnoldi †A. g. daudinii A. g. hololissa) †Aldabrachelys abrupta †Aldabrachelys grandidieri
Astrochelys	Angonoka tortoise Radiated tortoise †Astrochelys rogerbouri
Centrochelys	African spurred tortoise †Centrochelys atlantica †Centrochelys burchardi †Centrochelys vulcanica
Chelonoidis	Chaco tortoise Red-footed tortoise Yellow-footed tortoise †Chelonoidis alburyorum †Chelonoidis cubensis †Chelonoidis lutzae †Chelonoidis monensis †Chelonoidis sellovii †Chelonoidis sombrerensis
Galápagos tortoise Chelonoidis complex	Cerro Azul giant tortoise Chatham Island giant tortoise Eastern Santa Cruz tortoise Fernandina Island tortoise †Floreana Island tortoise Hood Island giant tortoise (Diego) Santa Fe Island tortoise †Pinta Island tortoise †(Lonesome George) Santiago Island giant tortoise Pinzón Island giant tortoise Sierra Negra giant tortoise Volcán Alcedo giant tortoise Volcán Darwin giant tortoise Volcán Wolf giant tortoise Western Santa Cruz tortoise
†Cheirogaster	†Cheirogaster bacharidisi †Cheirogaster gymnesica †Cheirogaster schafferi
Chersina	Angulate tortoise
Chersobius	Nama padloper Karoo padloper Speckled padloper
†Cylindraspis	†Domed Mauritius giant tortoise †Domed Rodrigues giant tortoise †Réunion giant tortoise †Saddle-backed Mauritius giant tortoise †Saddle-backed Rodrigues giant tortoise
Geochelone	Burmese star tortoise Indian star tortoise
Gopherus	Bolson tortoise Desert tortoise Goode's thornscrub tortoise Gopher tortoise Sonoran Desert tortoise Texas tortoise
†Hadrianus	†Hadrianus corsoni †Hadrianus majusculus †Hadrianus octonaria †Hadrianus robustus †Hadrianus schucherti †Hadrianus utahensis †Hadrianus vialovi
†Hesperotestudo	†Hesperotestudo percrassa
Homopus	Common padloper Greater padloper
Indotestudo	Elongated tortoise Forsten's tortoise Travancore tortoise
Kinixys	Bell's hinge-back tortoise Forest hinge-back tortoise Home's hinge-back tortoise Lobatse hinge-back tortoise Natal hinge-back tortoise Speke's hinge-back tortoise
Malacochersus	Pancake tortoise
Manouria	Asian forest tortoise Impressed tortoise
†Megalochelys	†Megalochelys atlas †Megalochelys cautleyi †Megalochelys margae †Megalochelys sondaari
Psammobates	Geometric tortoise Serrated tortoise Tent tortoise
Pyxis	Flat-backed spider tortoise Spider tortoise
Stigmochelys	Leopard tortoise
†Stylemys	†Stylemys botti †Stylemys calaverensis †Stylemys canetotiana †Stylemys capax †Stylemys conspecta †Stylemys copei †Stylemys emiliae †Stylemys frizaciana †Stylemys karakolensis †Stylemys nebrascensis †Stylemys neglectus †Stylemys oregonensis †Stylemys pygmea †Stylemys uintensis †Stylemys undabuna
Testudo	Hermann's tortoise Kleinmann's tortoise Marginated tortoise Spur-thighed tortoise †Testudo brevitesta
Phylogenetic arrangement of turtles based on turtles of the world 2017 update: Annotated checklist and atlas of taxonomy, synonymy, distribution, and conservation status. Key: †=extinct.