Neurotechnology Numbers Worth Knowing

April 28, 2022, updated March 20, 2023

In the tradition of Cell Biology by the Numbers, Physiology by Numbers, and Latency Numbers Every Programmer Should Know, here’s a collection of numbers worth knowing if you’re working in neurotechnology.

You can also download this list as Anki flashcards. Having them memorized and at your fingertips is great for sanity checking ideas.

I plan to keep growing this list and Anki deck in perpetuity, so if it’s missing your favorite numbers, please let me know!

Thanks to Eemaan Thind, Max Hodak, Sumner Norman, Sam Rodriques, Mackenzie Dion, and Raffi Hotter for contributions.

The Numbers

General Orientation

A human hair is ~50 um in diameter.
1 angstrom equals 0.1 nm.
The C-H bond length is ~1 angstroms.
The covalent radius of Hydrogen is ~30 pm. The covalent radius of Caesium is ~250 pm.
A water molecule is ~0.25 nm across.
A glucose molecule’s mass is ~180 g/mol, and its cyclic form would fit comfortably in a 1nm diameter sphere.
1 mm equals 3 French
The abundance-weighted average mass of an amino acid in humans is ~110 g/mol.
Viruses range in size from 10s to 100s of nm in diameter.
Viral genomes range in length from 1s to 100s of kbs.
AAVs are ~25 nm in diameter and contain ~4.7 kb of single-stranded DNA.
E. coli is ~1 um in diameter and ~2 um long, with a volume of ~1 um^3.
C. elegans has ~300 neurons and is ~1mm long.
A doubles tennis court is ~3000 ft^2.

1 mm^3 equals 1 uL.
1 M concentration is ~1 particle per 1 nm^3.
1 nM concentration is about ~1 particle per 1 um^3.
The density of water is 0.99 g/ml at 1 atm and body temperature.
Healthy average human body temperature is ~37°C, with variations of +- ~1°C between individuals and within individuals throughout the day. (source)
Room temperature is ~25°C.
A medium-sized apple weighs ~1 Newton and exerts ~500 Pa of pressure on your palm.
A slightly overinflated road bike tire is at ~1 MPa of pressure.
Humans can hear sounds from 20 to 20,000 Hz and above 20 uPa of pressure.
The Svedberg is defined as 10^−13 s.

The Earth’s magnetic field at its surface is ~50 uT. (source)
A fridge magnet is ~10 mT. (source)
The FCC limit for public exposure from cellular telephones is an SAR level of 1.6 W/kg. The peak power output of a cell phone is on the order of 1s of W. (source)
Average US electricity price is ~10¢ / kWh.

Gamma and X-rays have wavelengths < ~1nm and frequencies > ~300 PHz.
UV spectrum has wavelengths between 1 nm and 380 nm and frequencies between 300 PHz and 790 THz.
Visible spectrum has wavelengths between 380 nm and 750 nm and frequencies between 790 THz and 400 THz.
IR spectrum has wavelengths between 750 nm and 1 mm and frequencies between 400 THz and 300 GHz.
Microwave spectrum has wavelengths between 1mm and 1m and frequencies between 300 GHz and 300 MHz.
Radio spectrum has wavelengths >1m and frequencies <300 MHz.

Time period between conscious intention and action is ~200 ms. (source)
Human response times on simple reaction time tasks are ~200 ms.
Information transfer rate for typing is ~250 bits/min (50 wpm conversational texting speed x ~5 char/word x ~1 bit/char) and ~3000 bits/min for speaking. (Partially derived from source)
The fast (16th) synth notes in Darude’s Sandstorm (the notes you’d sing if you were trying to sing Sandstorm to someone) are ~10Hz.

Structural

The human brain weighs ~1.5 kg.
The brain is between ~75% water by mass. (source)
Intracranial volume is ~1700 mL, consisting of ~1400 mL (80%) of brain, ~150 mL (10%) of blood, and ~150 mL (10%) of CSF. (source)
The brain’s interstitial system accounts for ~20% of brain volume. (source)
Intracranial pressure is between 1-2 kPa. (source)
Normal human blood pressure is 120/80 mmHg (systolic/diastolic), or 16/10 kPa. (source)
Interruption of cerebral blood flow results in loss of consciousness within 10s. (source)
Only ~25% of people have a fully intact Circle of Willis. (source)

Capillaries make up ~85% of the vasculature of the brain. (source)
The arteries in the Circle of Willis are between 2-4 mm in diameter. (source)
Brain capillaries are ~7 um in diameter. (source)
The mean intercapillary distance in the human brain is ~40um, which is room for ~2 neurons. (source)
The average human adult has ~5 liters of circulating blood. (source)
Normal values for complete blood count are between 4M-6M RBC/uL, between 100k-300k platelet/uL, between 5k-10k WBC/uL, and between 35-50% hematocrit. (source)
The average density of human blood is ~1.06 g/mL. (source)
The entire volume of CSF is produced between 4-5 times per day in the human brain. (source)
Healthy human resting heart rate is between 1-2 Hz.
Cerebral displacement with heartbeat is on the order of 100s of um, varying by region. (source)
In the aorta, peak blood velocity is ~1 m/sec. (source) As blood moves into the capillary beds, the rate of movement slows to ~1 mm/sec. (source)
~94% of cerebral oxygen consumption is by gray matter. (source)
The basal metabolic rate of a human is ~1500 kcal or ~6 MJ per day. (source)
The safe range of temp increase of human brain tissue is up to ~3°C. (source)
Human brain temperature at the periphery is about equal to body temperature, and rises up to 1°C higher in the deep brain. (source)
The volume of the human body is ~50 L.
The surface area of the body covered by skin is ~2 m^2. (source)
The surface area of the body’s mucous membranes (digestive, respiratory, reproductive) is ~400 m^2. (source)

Young’s modulus of brain is between 0.1-16 kPa. (source)
Young’s modulus of connective tissues and arteries are between 0.1–1 MPa. (source)
Young’s modulus of bone is between 15–30 GPa. (source)
Speed of sound is ~1480 m/s in water. (source)
Speed of sound is ~1500 m/s in brain tissue. (source)
Speed of sound is ~2100 m/s in trabecular bone. (source)
Speed of sound is ~2800 m/s in cortical bone. (source)

The resistivity of air is ~10^15 Ω⋅m. (source)
The resistivity of dry skin through the epidermis is ~10k Ω⋅m. (source)
The resistivity of (wet) scalp is ~2 Ω⋅m. (source)
The resistivity of fat is ~40 Ω⋅m. (source)
The resistivity of skull is ~100 Ω⋅m. (source)
The resistivity of CSF is ~0.5 Ω⋅m. (source)
The resistivity of gray matter is ~4 Ω⋅m. (source)
The resistivity of white matter is ~8 Ω⋅m. (source)

Cellular

There are ~85 B neurons and about the same number of glia in the whole brain. (source)
The cortex (GM + WM, everything outside the striatum) has ~15 B neurons and ~60 B glia; that’s ~80% of the brain’s mass and ~20% of the brain’s neurons. (source)
The cerebellum has ~70 B neurons and ~15 B glia; that’s ~10% of the mass and ~80% of the neurons. (source)
The non-cortex-non-cerebellum part of the brain has ~1 B neurons and ~10 B glia; that’s ~10% of the mass and ~1% of the neurons. (source)
Gray matter has ~20 B glia, while white matter has ~40 B glia. (source)
Gray matter has ~12 B neurons, while white matter has ~3 B neurons. (source)
There are ~150 trillion synapses in cortex. (source)
~88% of neurons in the brain are granule cells. (source)
Only ~500k neurons in the brain produce dopamine.
Serotonin is produced by ~100k neurons in the brainstem. Serotonergic neurons project so widely that virtually every neuron in the brain may be contacted by a serotonergic fiber.
Histamine is exclusively synthesized by ~65k neurons per side in the hypothalamus, projecting everywhere in the CNS.
The locus ceruleus contains ~25k norepinephrine neurons per side, providing virtually all the norepinephrine to the cortex and accounting for ~50% of all norepinephrine neurons in the brain.

Total surface area of the cerebral cortex is ~2500 cm^2. (source)
The surface area of the cerebellar cortex is ~1590 cm^2. (source)
Thickness of cortical gray matter is ~2.5 mm on average, ranging between 1-4.5 mm by region. (source)
A mm^3 of cortex contains on the order of 10s of thousands of neurons. (derived)
Cortical minicolumns contain between 80–100 neurons, spanning all cortical layers, with a diameter of approximately 30–50 um. (source)

Delta waves are between 0–4 Hz, prominent in deep sleep, associated with motivation. (source)
Theta waves are between 4–8 Hz, prominent in deep sleep, associated with memory and prefrontal cognitive processes. (source)
Alpha waves are between 8–13 Hz, prominent when eyes are closed or when drowsy/relaxed, associated with cognitive inhibition. (source)
Mu waves are between 7.5–12.5 Hz, prominent in motor cortex when body is physically at rest, suppressed by motor actions. (source)
Beta waves are between 13–30 Hz, prominent in frontal/central regions when alert and active, associated with motor control. (source)
Gamma waves are between 30–70 Hz, prominent in frontal regions when engaged in higher cognitive processing, associated with short-range cortical feedback loops and activity of fast-spiking inhibitory interneurons. (source)

Diameters of neuron somas are between 5-100 um. (source)
There can be between 10^2-10^5 synapses per neuron, varying by neuron type.
The lifespan of a red blood cell is ~127 days. (source)
Red blood cells are ~8um in diameter and ~2um thick. (source)
The death rate of neocortical neurons in adult is ~1 per second. (source)
To reach the brain auditory stimuli take between 8-10 ms. (source)
To reach the brain visual stimuli take between 20-40 ms. (source)
There are ~100M photoreceptors per human retina and ~1M nerve fibers per optic nerve.
The human spinal cord contains ~200M neurons and ~1B glia. (source)
Short term plasticity lasts milliseconds to minutes.
Long-term potentiation/depression lasts minutes to months.
Between 25-75% of neurons are “dark” (never observed firing) in ephys studies, though this varies widely. (source)
Successful spike transmission rates between 10-90% are widely reported in the literature. (source)

Intracellular

An alpha helix has ~3.5 residues per turn and rises ~0.5 nm per turn.
Strands in a beta sheet are ~0.5 nm apart.
mRNA comprises between 1–5% of the total RNA in a typical mammalian cell.
There are 9 essential amino acids for humans.
There are 21 proteinogenic amino acids in eukaryotes.
There are 20 amino acids in the standard genetic code.
Proteins and macromolecules occupy between 20-30% of the cytosolic volume. (source)
There are ~200M hemoglobin molecules per red blood cell. (source)
Diameters of neuron nuclei are between 3-18 um. (source)
A nuclear pore complex moves a protein in or out of the nucleus at a frequency of ~1 kHz. (source)
The mass of a base pair in DNA (2 nucleosides and 2 phosphates) is ~650 g/mol.
The DNA double helix has a diameter of ~2 nm.
A nucleosome is ~10 nm in diameter, with ~150 base pairs wrapped around it.
If stretched out, a human cell’s DNA would be ~3 meters in length. (source)
The typical mRNA half life in human cells is ~10 hours. (source))
The ribosome has a diameter of between 20-30 nm and a mass of ~2.5 MDa.
Higher eukaryotic ribosomes have a mass of ~4.5 MDa.
Organellar ribosomes have a mass of ~2.5 MDa.
A microtubule is ~25nm in diameter.
Fast anterograde and retrograde transport down cytoskeleton is between 1-4 um/s. Slow transport down cytoskeleton is 1-30 nm/s - though really it’s saltatory, not slow.
~30 ATP molecules are generated from full oxidation (all pathways) of one molecule of glucose. (source)
Mitochondria vary widely in shape and over two orders of magnitude in size but are on the order of 1um.
Cell membranes are between 4-6 nm across.
The cell membrane area is ~50% protein and the remainder lipid.
GPCRs are between 50-100 kDA in mass, ~500 AAs long, and their transmembrane domains are between 6-8 nm “tall.”
Large dense core vesicles are between ~100 nm in diameter.
Synaptic vesicles are ~40 nm in diameter, or ~10^-5 um^3 in volume.
There are between 10^3-10^4 neurotransmitter molecules in each synaptic vesicle.
Distance across the synaptic cleft is between 20-40 nm.
The surface area of synapses vary widely in shape and over 3 orders of magnitude in size, with a mean area ~75k nm^2. (source)
It takes on the order of 10s for a protein to diffuse 20 um in a cell. (source)

The resting membrane potential of a neuron ranges between -40 and -90 mV in healthy human neurons. On average it’s ~ -70mV and the firing threshold is ~ -55 mV. (source)
Biological membranes have a capacitance of ~1 uF/cm^2. (source)
In the exocytotic cycle, the vesicle fusion and release takes ~1ms; endocytosis takes between 10-1000 ms; recycling, neurotransmitter transport, docking, priming take 10-60s.
A sodium–potassium pump transports 3 Na+ ions out of the cell and 2 K+ ions in at a time.
A single sodium-potassium pump’s maximum transport rate is ~200 Na ions/s and ~130 K ions/s.
It takes ~1 ms for a neurotransmitter to diffuse across the synaptic cleft.
ACh receptors open transiently for between 1-10ms on ACh binding.
During an axonal action potential, the membrane depolarizes in ~1 ms and returns to the resting value in the next betewen 1-2 ms. (source)
Conduction velocity down an axon in peripheral nerve is ~50 m/s, ranging between 0.5-120 m/s depending on nerve type. (source)
Action potential durations vary depending on cell type, but in the brain are generally between 1-5 ms. (source)
GCaMP8m has a time to peak of ~20ms and peak delta F/F of ~1 for one action potential. (source)

Genetic

There are 23 pairs of chromosomes in the nucleus of a somatic human cell.
There are 3.2 billion base pairs in a haploid human genome.
The human genome is ~1.5% coding exons, ~25% introns, and the rest non-intron noncoding.
There are ~45,000 genes in the haploid human genome, of which ~20,000 are protein-coding genes.
There are ~17,000 base pairs in and 13 proteins encoded by the mitochondrial human genome.
The median human gene contains 7 exons and the average length of introns is ~3 kb, though this varies widely. (source)
There are ~800 GPCRs encoded by the human genome, about 50% of which are olfactory receptors. (source)
RNA polymerases make one mistake for every ~10^4 nucleotides transcribed.
Rate of DNA replication is ≤ ~2 kb/min, which is the rate at which replication forks plow through chromatin. (source)
Spacing between origins of DNA replication is ~100 kb. (source)
There are ~1^-8 mutations per base pair per generation, or ~30 mutations per replication of haploid genome. (source)

Hardware

DBS leads are ~1.3 mm in diameter with currents on the order of 1s of mA. (source)
The smallest FDA-approved stent is ~2mm in diameter. (source)
Standard optical fibers for optogenetics are on the order of 100s of um in diameter. (source)
The diffraction limit of a visible light microscope is ~200 nm. (source)
Nominal bitrate of a USB 4.0 is 40 Gbit/s.
Bluetooth 2.0 nominal bitrate is 3.0 Mbit/s.
L1 cache ref takes ~1 ns. (source)
L2 cache ref takes ~4 ns. (source)
Main memory ref takes ~100 ns. (source)
Packet roundtrip CA to Netherlands will take ~150 ms. (source)
The fastest mobile SoCs as of 2022 are on the order of 100 mm^2 in size, TDPs on the order of 1s of W, and GPUs doing on the order of 1s of TFLOPS. (source)
Sequencing error rates range from 10%/base to 0.1%/base depending on method and hardware. (source)

Operational

Generic all-in lab space costs are ~$100/sqft/yr in science hubs (SFO, BOS, etc.) and ~$50/sqft/yr in non-hubs.
An 1-hr MRI scan costs on the order of $1k at a university.
A cage of 5 mice costs ~$1k upfront and ~$5k/yr recurring.
It’s ~$1M/yr for a minimum-viable macaque program. Smaller NHPs have far lower overhead. (source)
New drug development costs vary widely, but are on average $1B and 10 years from start to FDA approval.
Street prices for psychoactive drugs vary widely, but are on the order of 100s of $/g. (source)
Rule of thumb is that it takes 10k patient uses with no adverse effects for the FDA to allow a medical device to go OTC.
Total inpatient cost for fully invasive brain surgery is ~$50k. (source)
Total inpatient cost for fully invasive brain surgery including longer term care is ~$100k. (source)
In 2021, ~16% of the US population 12 or older had a substance use disorder. (source)
In 2017, substance use was responsible ~20% of deaths globally. (source)
In 2017, the most dangerous neurotechnologies were tobacco, 15% of global deaths, and alcohol, 4% of global deaths. Deaths from all other drug is ~1% of global deaths. (source)