Most searches that reach a gematria calculator are about a specific number someone encountered elsewhere. Here are the ones that come up most, with the sources, and with a straight answer where the honest answer is that there isn't one.
18 — chai, life
חי totals 18 in standard gematria. This is the most widely known value in Jewish practice and the reason charitable donations are commonly made in multiples of eighteen. The custom is well documented and current, which makes it the clearest example of gematria functioning as living tradition rather than speculation.
26 — the Tetragrammaton
יהוה totals 26. The number appears throughout Kabbalistic literature, often in combination with other values. Note that אהבה (love) and אחד (one) each total 13, and 13 + 13 = 26 — a construction cited frequently in Hasidic teaching to link love, unity and the divine name.
666 — Revelation, and the Nero reading
The number comes from Revelation 13:18, written in Greek numerals as χξϛ. The most widely held scholarly explanation is a Hebrew gematria: 'Neron Kesar', the Greek form of Nero Caesar transliterated into Hebrew letters as נרון קסר, totals 666 — nun 50, resh 200, vav 6, nun 50, qof 100, samekh 60, resh 200.
The strength of the reading is that it also explains the variant. Some early manuscripts, including Papyrus 115 and Codex Ephraemi Rescriptus, read 616 instead. The Latin spelling 'Nero Caesar' drops the final nun worth 50, giving exactly 616. Irenaeus knew of the 616 reading in the second century and argued against it. This remains an interpretation rather than a settled fact, but the fact that one spelling difference accounts for both numbers is why it is the standard scholarly view. The Greek numeral side of this is covered in more depth on our Greek gematria page.
777 — no traditional source
This is a case where the honest answer is that there isn't one. 777 has no established meaning in Jewish gematria and no rabbinic source assigns it particular significance. Its currency comes from modern numerological writing, usually as a counterpart to 666, and from English-system calculations where various phrases happen to total 777. If a source tells you 777 means something specific in gematria, ask which tradition and which text it is drawing on.
358 — mashiach and nachash
משיח (messiah) and נחש (serpent) both total 358. The equivalence is cited in Kabbalistic literature as a way of framing the messianic role against the serpent of Eden. It is a genuine example of the interpretive move gematria is used for: the numbers are offered to illustrate a theological reading, not to prove it.