<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2023-07-28</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001126956</issuerCik>
        <issuerName>SPIRE INC</issuerName>
        <issuerTradingSymbol>SR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001104955</rptOwnerCik>
            <rptOwnerName>KOONCE PAUL D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4112 OXFORD RD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>RICHMOND</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>23221</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>true</isDirector>
            <isOfficer>false</isOfficer>
            <isTenPercentOwner>false</isTenPercentOwner>
            <isOther>false</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>5.9% Series A Cumulative Redeemable Perpet. Preferred Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8846.00</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents depositary shares, each representing a 1/1,000th interest in a share of Spire Inc. 5.90% Series A Cumulative Redeemable Perpetual Preferred Stock, par value $25.00 per share, with a $25,000 liquidation preference (equivalent to $25.00 per depositary share) (the &quot;Series A Preferred Stock&quot;), deposited with Computershare Inc. and Computershare Trust Company, N.A., acting jointly, as depositary.  Holders of depositary shares are entitled to a proportional fractional interest in all rights and preferences of the Series A Preferred Stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Courtney Vomund as attorney in fact for Koonce, Paul D.</signatureName>
        <signatureDate>2023-08-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
