2,000,000,000 t4.41 × 10¹² lb
A 5 ml teaspoon of neutron star would weigh about 2 billion tonnes (4.4 trillion lb). That is our estimate, not a measured figure: a typical neutron star packs 1.4 Suns into a ball about 24 km across. Matter from the thin crust would weigh far less, and matter from the core up to about twice as much.
| From the deep coreEstimated 800 trillion kg per m³; nobody knows the core for sure | 4,000,000,000 t8.82 × 10¹² lb |
|---|---|
| Average of PSR J0740+6620Heaviest known neutron star: 2.1 Suns, about 24.8 km across | 2,600,000,000 t5.73 × 10¹² lb |
| Average of PSR J0437-47151.42 Suns, 11.4 km radius (NICER, 2024) | 2,300,000,000 t5.07 × 10¹² lb |
| Our estimate, typical neutron star1.4 Suns in a 12 km radius; 1.9 billion t before rounding | 2,000,000,000 t4.41 × 10¹² lb |
| Average of PSR J0030+04511.4 Suns, about 26 km across (NICER, 2019) | 1,500,000,000 t3.31 × 10¹² lb |
| From the outer crustAbout 1 billion kg per m³ | 5 t11,000 lb |
Nobody has ever scooped up neutron star matter, so the figure is our estimate, worked out from measured stars. NASA’s NICER X-ray telescope on the International Space Station has measured neutron stars of about 1.4 times the Sun’s mass with radii of roughly 11 to 13 km. We used 1.4 solar masses and a 12 km (7.5 mile) radius, a ball about 24 km (15 miles) across.
The arithmetic: 1.4 × 1.989 × 10³⁰ kg is about 2.8 × 10³⁰ kg. A sphere with a 12,000 m radius has a volume of 4/3 × π × 12,000³, about 7.2 trillion m³. Mass divided by volume gives an average density of about 385 trillion kg per cubic metre. A 5 ml teaspoon is 0.000005 m³, so it holds about 1.9 billion tonnes, which we round to 2 billion.
NASA rounds harder and says a teaspoon of neutron star matter would weigh a billion tons on Earth. Other popular figures go up to 5 or 6 billion tonnes because they assume denser matter from deeper inside the star. All of them agree on the scale: billions of tonnes in one spoon.
A neutron star is not equally dense all the way through. Density rises with depth, from about 1 billion kg per cubic metre in the crust to an estimated 600 to 800 trillion kg per cubic metre in the core. A teaspoon from the crust would weigh only about 5 tonnes (11,000 lb), while a teaspoon from the core would weigh 3 to 4 billion tonnes.
The average density is close to that of an atomic nucleus. What the core is made of is still an open question: NASA describes models with ordinary neutrons and protons, and others where part of the core is exotic matter made of quarks. Pinning that down is the main goal of NICER.
Neutron stars are not all alike, and the radius matters a lot because volume grows with its cube. PSR J0437-4715, the closest millisecond pulsar at about 510 light-years, has 1.42 solar masses in an 11.4 km radius, which works out to about 460 trillion kg per cubic metre and 2.3 billion tonnes per teaspoon.
PSR J0030+0451 has about the same mass but measured about 26 km across, so its average spoonful is lighter, about 1.5 billion tonnes. PSR J0740+6620, the heaviest neutron star known at about 2.1 solar masses, is roughly 24.8 km across, giving about 2.6 billion tonnes. These sizes carry uncertainties of several percent or more, and because the radius is cubed, the density uncertainties are about three times larger.
About 4.4 trillion lb, based on our estimate of 2 billion tonnes for a 5 ml teaspoon. NASA’s rounder figure of a billion tons is about 2 trillion lb.
On average, about 300 to 600 trillion kg per cubic metre, roughly the density of an atomic nucleus. NICER’s principal investigator Keith Gendreau compared it to squeezing Mount Everest into a sugar cube.
About 20 to 26 km (12 to 16 miles) across, the size of a city. NICER measured PSR J0437-4715 at a radius of 11.4 km.
A typical one has about 1.4 times the mass of the Sun, around 2.8 × 10³⁰ kg. The heaviest known, PSR J0740+6620, has about 2.1 solar masses.
Last checked October 2, 2026.
