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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-06-08</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000350077</issuerCik>
        <issuerName>WMS INDUSTRIES INC /DE/</issuerName>
        <issuerTradingSymbol>WMS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001200086</rptOwnerCik>
            <rptOwnerName>GAMACHE BRIAN R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O WMS INDUSTRIES INC.</rptOwnerStreet1>
            <rptOwnerStreet2>800 S. NORTHPOINT BLVD.</rptOwnerStreet2>
            <rptOwnerCity>WAUKEGAN</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60085</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman and CEO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-06-08</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2131</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>31.76</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>123837</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents a reduction in shares to satisfy the tax withholding obligation of the Company with respect to the vesting on 6/7/2009 of 7,235 shares of restricted stock held by Mr. Gamache.</footnote>
        <footnote id="F2">Includes 82,185 shares of restricted stock, for which restrictions will lapse on (a) 5,100 on each of 9/18/2009, 9/18/2010 and 9/18/2011 and 5,101 on 9/18/2012; (b) 17,036  on 9/18/2009 if certain performance goals are met, if not, such shares will vest on 9/18/2010 provided certain performance goals are met as of that date and 17,036 on 9/18/2010 if certain performance goals are met; (c) 4,413 on 9/19/2010 and 4,414 on each of 9/19/2009 and 9/19/2011; and (d) 7,235 on 6/7/2010 and 7,236 on 6/7/2011.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Brian R. Gamache</signatureName>
        <signatureDate>2009-06-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
