Mishnah for Kelim 5:1
תַּנּוּר, תְּחִלָּתוֹ אַרְבָּעָה, וּשְׁיָרָיו אַרְבָּעָה, דִּבְרֵי רַבִּי מֵאִיר. וַחֲכָמִים אוֹמְרִים, בַּמֶּה דְבָרִים אֲמוּרִים, בְּגָדוֹל. אֲבָל בְּקָטָן, תְּחִלָּתוֹ כָּל שֶׁהוּא, וּשְׁיָרָיו רֻבּוֹ, מִשֶּׁתִּגָּמֵר מְלַאכְתּוֹ. אֵיזֶהוּ גְמַר מְלַאכְתּוֹ, מִשֶּׁיַּסִּיקֶנּוּ כְּדֵי לֶאֱפוֹת בּוֹ סֻפְגָּנִין. רַבִּי יְהוּדָה אוֹמֵר, מִשֶּׁיַּסִּיק אֶת הֶחָדָשׁ, כְּדֵי לֶאֱפוֹת בַּיָּשָׁן סֻפְגָּנִין:
An oven's minimum size [to be able to become ritually impure] is four <em>tefachim</em> [handbreadths in height] and its remainder [that remains impure when it is broken] is four <em>tefachim</em>; the words of Rabbi Meir. The Sages say, this is only true regarding a large oven; regarding a small oven, however, it beginning [point] is any [size] and its remainder is a majority [of its size] once its manufacture has been completed. What is the completion of its manufacture? Once it is kindled enough to bake a sponge cake in it. Rabbi Yehudah says, once it is kindled enough to bake a sponge cake [as] in an old oven.