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

    <schemaVersion>X0305</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-03-30</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001029506</issuerCik>
        <issuerName>RALCORP HOLDINGS INC /MO</issuerName>
        <issuerTradingSymbol>RAH</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001413813</rptOwnerCik>
            <rptOwnerName>Wenzel David R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O RALCORP HOLDINGS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>800 MARKET STREET, SUITE 2600</rptOwnerStreet2>
            <rptOwnerCity>SAINT LOUIS</rptOwnerCity>
            <rptOwnerState>MO</rptOwnerState>
            <rptOwnerZipCode>63101</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Ralcorp Holdings, Inc. Stock Equivalents</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-03-30</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>97</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>74.09</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>$.01 Par Value Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>97</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>9455</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Reporting person's retainers and fees earned as a Director of Issuer are deferred into Ralcorp Holdings, Inc. Stock Equivalents under the Issuer's Deferred Compensation Plan for Non-Management Directors.  Reporting person is credited with stock equivalent as soon as administratively practicable following the month in which such retainers and fees are earned.  The value of these stock equivalents is distributed (on a one-for-one basis) in the form of cash upon retirement from the Board of Directors.</footnote>
        <footnote id="F2">The stock equivalents have no fixed exercisable or expiration dates.</footnote>
        <footnote id="F3">Fractional shares credited monthly are reflected in the end of month total.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Gregory A. Billhartz, Attorney-in-Fact for David R. Wenzel</signatureName>
        <signatureDate>2012-04-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
