Intracellular fluidThe fluid inside the cells. It holds about two thirds of the body's water.
Extracellular fluidAll the fluid outside the cells. It holds about one third of the body's water.
Total body waterAll the water in the body. The fluid inside and outside the cells adds up to it.
Blood plasmaThe liquid part of blood. It is the extracellular fluid inside the blood vessels.
Interstitial fluidThe fluid between the cells of a tissue. It is the larger part of the extracellular fluid.
Cell membraneThe barrier around every cell. It separates the fluid inside the cells from the fluid outside.
Capillary wallThe wall of the smallest blood vessels. It separates blood plasma from the fluid around the cells; water and salts cross it.
Transcellular fluidSmall pools set apart from the rest. Cerebrospinal fluid, joint fluid and the fluid in the eye are examples.
Solids and fluids 3
ProteinLong chains of amino acids. It is one of the three solids beside the bar.
FatThe lipids among the body's solids. Fat tissue stores energy in this form.
MineralsSolids such as the calcium salts in bone. Calcium phosphate is the chief salt of bone.
How this list was compiled: Every name and every share read on 2026-10-03 and kept only where two independent sources give it. (1) Wikipedia, text only: Fluid compartments, Body water, Extracellular fluid and Composition of the human body, https://en.wikipedia.org/wiki/Fluid_compartments and https://en.wikipedia.org/wiki/Body_water . (2) Peruzzo and others, Body fluids and salt metabolism, Part I, Italian Journal of Pediatrics 35:36 (2009), open access, https://europepmc.org/article/PMC/PMC2784783 : total body water, the intracellular compartment with about two thirds of it, the extracellular compartment, its interstitial and intravascular parts, the transcellular fluids, the cell membrane and the capillary membrane. (3) Wikibooks, Human Physiology, Homeostasis, https://en.wikibooks.org/wiki/Human_Physiology/Homeostasis : plasma and interstitial fluid as the two parts of the extracellular fluid, beside the fluid in the cells. (4) Ganong, Review of Medical Physiology (1973), read by full-text search on archive.org, https://archive.org/details/reviewofmedicalp0001gano : protein, mineral and fat as the solids of a young adult, and water as 60% of body weight. (5) For the three captions beside the solids: MedlinePlus Genetics (U.S. National Library of Medicine), What are proteins and what do they do?, https://medlineplus.gov/genetics/understanding/howgeneswork/protein/ : proteins are made up of amino acids; U.S. National Cancer Institute, SEER Training Modules, Introduction to the Skeletal System, https://training.seer.cancer.gov/anatomy/skeletal/ : the matrix of bone holds large amounts of calcium salts, calcium phosphate above all; Karimi and others, Metabolites 14:336 (2024), open access, https://europepmc.org/article/PMC/PMC11205672 : fat tissue stores energy as triacylglycerols; and Wikipedia, Protein, Adipose tissue, Bone mineral and Body composition (fat, water, protein and mineral as the compartments of body mass). The chart is our own. Licence: own work
The drawing: Drawn for this site on 2026-10-03 from plain geometry; the blank tags are placed from the answer table. Own original chart; nothing traced or copied. Licence: own work
How it works
The first chart sorts the body's water into its compartments, with the two barriers between them. The second is a bar of body mass split into fluid and solids. Each box says what it holds, under its name; the quiz blanks the names.
Read the full guide
The compartments
Start at the wide box, total body water. Under it the left box is the intracellular fluid and the right box the extracellular fluid, which is found in three places: interstitial fluid, blood plasma and transcellular fluid. The dashed lines are the barriers, the cell membrane and the capillary wall.
Solids and fluids
The upper part of the bar is water, inside and outside the cells. The lower part is the solids: protein, fat and minerals, each beside a caption that says what it is. The chart does not rank the three.
Questions and answers
What are the fluid compartments of the body?
Two main ones. Intracellular fluid is the water inside the cells, about two thirds of the total. Extracellular fluid is the water outside them: interstitial fluid between the cells, blood plasma in the vessels and small amounts of transcellular fluid.
What separates the fluid compartments?
Cell membranes separate the intracellular fluid from the extracellular fluid. The walls of the capillaries separate blood plasma from interstitial fluid. Water crosses both.
How much of the body is water?
About 60% of an adult's body mass, though the share varies with age, sex and body fat. The rest is solids: protein, fat and minerals.
How do I label the water compartments of the body?
Start with total body water and split it in two: intracellular fluid inside the cells and extracellular fluid outside. Then split the extracellular fluid into interstitial fluid and blood plasma. The chart here is the site's own drawing.
Where do I drag the labels to identify the solid and fluid components in the human body?
On a bar of body mass the fluid part is water, inside and outside the cells, and the solid part is protein, fat and minerals. The second chart here is that bar.