Nitrogen abundance is one of the most uncertain among all elements in the Earth's interior. Recent data indicate an affinity between Fe‐nitrides and Fe‐carbides in the Earth's mantle and inner core. In this work P‐V‐T equations of state of ε‐Fe3N0.8 and ε‐Fe3N1.26 (which is close to Fe7N3) have been determined using a combination of multianvil and synchrotron radiation techniques at pressures up to 30 GPa and temperatures up to 1473 K. A fit of the P‐V‐T data to the Vinet‐Rydberg and Mie‐Grüneisen‐Debye equations of state yields the following thermoelastic parameters for the ε‐Fe3N0.8: V0 = 81.44(2) Å3, KT0 = 157(3) GPa, KT′ = 5.3 (fixed), θ0 = 555 K (fixed), γ0 = 1.83(1), and q = 1.34(18). For ε‐Fe3N1.26 we obtained V0 = 86.18(2) Å3, KT0 = 163(2) GPa, KT′ = 5.3(2), θ0 = 562(90) K, γ0 = 1.85(2), and q = 0.55(24). It is likely that all presumably paramagnetic ε‐Fe3Nx with x = 0.75–1.5 have similar thermoelastic properties with a minor increase of the bulk modulus with increasing N content. The melting temperature of ε‐Fe3Nx increases from approximately 1473 to 1573 K in the pressure range from 5 to 30 GPa. We also determined a preliminary equation of state for γ‐Fe4Ny and calculated y = 0.35(2) from the data at 20–30 GPa. Combining the results with a recent experimental study on the stability of β‐Fe7N3, isostructural with Fe7C3, and a theoretical study of the magnetic transitions in ε‐Fe3Nx, we estimate the density of Fe‐nitrides at the Earth's inner core conditions. Our results indicate that at 5000–6000 K, 2.0–3.2 wt % N can explain the density deficit in Earth's inner core.