Is the count the number of guests?

No. Order one invitation for each household that shares an address. Two parents at one house are one card. An adult cousin in another apartment is another card.

Do children get their own invitation?

Children who live at home are named on the household card if they are invited. They do not need a second envelope unless they live somewhere else.

What if one event has more guests than another?

Count each card you will actually mail or hand over. The ceremony stack and the sangeet stack can be different numbers. Do not add the lists together when both cards go in one envelope to the same house.

How many wedding invitations to order

Start with a list of mailing addresses, not a list of names on a spreadsheet. An invitation goes to a household. A seat, a meal, and a plus-one are guest-list problems, and they are handled in RSVP and guest management. The print order is about envelopes.

Build the household list

Write one line per address.

A couple who live together is one invitation, even though two people are invited. Both names go on the envelope. How to write those names is in envelope addressing.
Parents who do not live with you are their own household.
An adult sibling with a separate lease is a separate household.
A grandparent who lives with an aunt is part of that aunt's household, unless you are handing them a card in person and want them to have their own.
Children at home are guests, not a second mailing. Name them on the inner card or the envelope if they are invited. If they are not invited, do not write "and family."
A plus-one who does not have a name yet is not an extra household. It is a phrase on the invited guest's card, and only if you are truly offering one.

Read the list once and cross off anyone you are not going to invite. A save-the-date already promised them a card. If you sent one, this household stays. That rule is in save-the-date etiquette.

Count cards, not just envelopes

Photo coming soon

A photograph of separate stacks of ceremony cards and smaller event inserts, counted one set per household.

A South Asian wedding in the US rarely has one list.

Count ceremony envelopes. That is the number of ceremony invitations.
Count mehndi, sangeet, and reception households separately.
If a household is invited to two events and both cards will travel in one envelope, you still need both cards, and you need one outer envelope.
If you mail the sangeet card on its own to people who are not invited to the ceremony, those are extra envelopes and extra cards.
Details inserts, such as hotels and the weekend schedule, usually match the ceremony envelope count, because everyone who gets the main card needs the practical note.

The wording for which event sits on which card is in invitation wording and mehndi, sangeet, and reception cards.

Spare cards, without a formula

Keep a short extra stack. Use it for a misspelled envelope, a household you add after a parent calls, and one set you want to keep. There is no reliable percentage that fits every wedding. A short guest list and a list that fills a hall do not need the same cushion.

Order the spare cards in the same print run. A later run can mean a separate proof and, for letterpress, another wait while ink is ordered. The timing is in the stationery timeline.

What the product pages already say

Each piece shows its own minimum on the product page. Do not assume the ceremony card and the insert share a minimum.

Flat invitations and metallic-foil invitations say that orders above 250 are quoted. If your household count is in that range, use the custom quote before you promise a mail date. The invitation catalog and the inserts are the pages those minimums live on.

Reply cards only need to exist for households who will reply on paper. If replies are collected on the RSVP page, you can skip a paper reply card and still print the invitation. Do not order a reply card for every guest on the list. Order one per household that is returning a paper card, or skip them.