\definemeasure[h1][1.2\measured{w1}+26mm]
> \definemeasure[h2][1.2\measured{w2}+26mm]

\measured gives me this error (Undefined control sequence):

\17>>h1 ^^@-1.2\measured
                       {w1}+26mm
\measure ...sname \csname \??measure #1\endcsname
                                                  \else \zeropoint \fi
\page_layouts_synchronize ...tparameter \c!height
                                                  }\ifx \p_page_layouts_heig...
<inserted text> ...yout \previouslayout \page_layouts_synchronize
                                                  \page_layouts_check_next \...
\setup_layout ...out :}[#1]\the \everysetuplayout
                                                  \the \everyswitchlayout \l...
\syst_helpers_double_empty_one_spaced ...1[{#2}][]

I am using ConTeXt  ver: 2013.04.20. So I tried to use \dimexpr:

\definemeasure[h1][\the\dimexpr 1.2\measure{w1}+26mm\relax]
\definemeasure[h2][\the\dimexpr 1.2\measure{w2}+26mm\relax]

but it gives me this error (there is a problem with the decimal point in 1.2 because there is no error when I put an integer instead):

\17>>w1 .-0.
            7500\paperwidth
\measure ...sname \csname \??measure #1\endcsname
                                                  \else \zeropoint \fi
\17>>h1 r-\the \dimexpr 1.2\measure {w1}
                                         + 26mm \relax
\measure ...sname \csname \??measure #1\endcsname
                                                  \else \zeropoint \fi
\page_layouts_synchronize ...tparameter \c!height
                                                  }\ifx \p_page_layouts_heig...