How flat is the Universe?

In order to answer this question, we combine ten independent astrophysical constraints in the space of the density parameters ${\mathrm{\Omega }}_m$ of gravitating matter and ${\mathrm{\Omega }}_{\mathrm{\Lambda }}$ of vacuum energy. We find that $\Omega_m=0.31\pm 0.07$,$\Omega_{\Lambda}=0.63\pm 0.21$,andthus$\Omega_m + \Omega_{\Lambda}=0.94\pm 0.22$\mathrm{.}Thetotal$\chi^2$ is 4.1 for 8 degrees of freedom, testifying that the various systematic errors included are generous. We also determine ${\mathrm{\Omega }}_m$ in the exactly flat case. Five supplementary flat-case constraints can then be included in our fit, with the result ${\mathrm{\Omega }}_m=1-{\mathrm{\Omega }}_{\mathrm{\Lambda }}=0.337\pm 0.031$. It follows that the age of the Universe is $t_0=13.5\pm 1.3$ (0.68/h) Gyr.