  We study the combined constraints on the compactification scale 1/R and the
Higgs mass m_H in the standard model with one or two universal extra
dimensions. Focusing on precision measurements and employing the
Peskin-Takeuchi S and T parameters, we analyze the allowed region in the (m_H,
1/R) parameter space consistent with current experiments. For this purpose, we
calculate complete one-loop KK mode contributions to S, T, and U, and also
estimate the contributions from physics above the cutoff of the
higher-dimensional standard model. A compactification scale 1/R as low as 250
GeV and significantly extended regions of m_H are found to be consistent with
current precision data.
