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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-11-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001069533</issuerCik>
        <issuerName>RGC RESOURCES INC</issuerName>
        <issuerTradingSymbol>RGCO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001282618</rptOwnerCik>
            <rptOwnerName>SMOOT RAYMOND D JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>P. O. BOX 13007</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ROANOKE</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>24030</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2019-11-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>78.447</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>29.74</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>38918.17</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Purchase made with optional cash contribution pursuant to the RGC Resources, Inc. Dividend Reinvestment and Stock Purchase Plan.</footnote>
        <footnote id="F2">38,543.170 shares owned directly by insider.  Includes 119.005 restricted stock shares purchased through dividends reinvested in the Restricted Stock Plan for Outside Directors of RGC Resources, Inc. and 32.371 unrestricted shares purchased through dividends reinvested in the Dividend Reinvestment and Stock Purchase Plan for RGC Resources, Inc.  375 shares owned indirectly by spouse.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Raymond D. Smoot, Jr. by Howard T. Lyon, POA dated 08/01/2018</signatureName>
        <signatureDate>2019-11-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
