Related for Terumot 1:7
אֵין תּוֹרְמִין, לֹא בְמִדָּה, וְלֹא בְמִשְׁקָל, וְלֹא בְמִנְיָן. אֲבָל תּוֹרֵם הוּא אֶת הַמָּדוּד וְאֶת הַשָּׁקוּל וְאֶת הַמָּנוּי. אֵין תּוֹרְמִין בְּסַל וּבְקֻפָּה שֶׁהֵם שֶׁל מִדָּה, אֲבָל תּוֹרֵם הוּא בָהֶן חֶצְיָן וּשְׁלִישָׁן. לֹא יִתְרֹם בִּסְאָה חֶצְיָהּ, שֶׁחֶצְיָהּ מִדָּה:
One may not set aside <i>Terumah</i> by measure, by weights, or by number. However, one may set aside <i>Terumah</i> from that which has been measured, weighed, or counted. One may not set aside <i>Terumah</i> in a basket or container with a known measure. However, one may set aside <i>Terumah</i> in them [by only filling them] a half or a third. One may not set aside <i>Terumah</i> in [a container that holds one] <i>Seah</i> [specific unit of volume, by only filling it] a half, since half of it is a measure.