The universe as a whole? I did find this......
https://www.forbes.com/sites/startswithabang/2018/07/14/ask-ethan-how-large-is-the-entire-unobservable-universe/#410c447ddf80
extract:
"This means the unobservable Universe, assuming there's no topological weirdness, must be at least 23 trillion light years in diameter, and contain a volume of space that's over 15 million times as large as the volume we can observe. If we're willing to speculate, however, we can argue quite compellingly that the unobservable Universe should be significantly even bigger than that".
Now we want to calculate a black hole with Cosmic Microwave Radiation inside (T_cmb = 2.725 K) {this gives a maximum possible radius of an universe}:
Energydensity Epsilon = atilde*T_cmb^4 = 4.1718e-14 [J/m^3] = 3*c^4/(8*pi*G*Rs^2) see GRT
This is a Schwarzschild-Radius of: Rs = sqrt(3*c^4/(8*pi*G*atilde*T_cmb^4)) = 1.8609e28 [m]
A Schwarzschild-Time of: ts = Rs/c = 1967 Gyr = 6.2073e19 The Mass of this black hole is: Ms = Rs*c^2/G = 2.5059e55 [kg] The density of the Photons within CMBR is: n_gamma = 16*pi*zeta(3){k*T_cmb/(h*c)}^3 = 410.5e6 [1/m^3] The total Photonnumber: N = 4*pi*Rs^3/3 * 410.5e6 = 1.1081e94 = const (primordial photons)!!! This black hole has a accelleration of: as = G*Ms/Rs^2 = 4.8296e-12 [m/s^2] = c/ts = dF / Ms The proof gives: Rs*as = c^2 (with is expected)