What is a sister-in-law?
A sister-in-law is your spouse's sister or your sibling's wife — both senses are standard, and one person can be both at once in a close family. The relationship is affinal, created by marriage: you share no ancestor, and the title formally lasts as long as the marriage that created it.
Relationship
Sister-in-law
- You
- Your spouse
- Their sister
From the other side, you are their sibling-in-law.
This connection runs through a marriage, not a shared ancestor, so the ancestor chart can't draw it.
The calculator below works out blood relationships through a shared ancestor — use it to explore the rest of your tree.
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This relationship sits outside the shared-ancestor model, so the card above carries the answer and the calculator opens in its default state. Work out any blood relationship with it, or open the full relationship calculator.
FAQs
Is my brother's wife my sister-in-law?+
Yes — and so is your spouse's sister. One word covers both marriage routes.
Is my husband's brother's wife my sister-in-law?+
Strictly she is your co-sister-in-law — two marriages sit in that chain — though many families stretch 'sister-in-law' to cover her.
Does the calculator store my family details?+
No — it runs entirely in your browser. Nothing you enter is uploaded or saved on our servers.
Start with one relative and see what comes back.
Add what you remember and AncestorIQ searches for the rest. Free to build your tree for as long as you like.
No credit card needed. Your tree stays yours.
