  We compute the D0-brane tension in string field theory by representing it as
a tachyon lump of the D1-brane compactified on a circle of radius $R$. To this
aim, we calculate the lump solution in level truncation up to level L=8. The
normalized D0-brane tension is independent on $R$. The compactification radius
is therefore chosen in order to cancel the subleading correction $1/L^2$. We
show that an optimal radius $R^*$ indeed exists and that at $R^*$ the
theoretical prediction for the tension is reproduced at the level of $10^{-5}$.
As a byproduct of our calculation we also discuss the determination of the
marginal tachyon field at $R\to 1$.
