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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2015-05-01</periodOfReport>

    <dateOfOriginalSubmission>2015-05-04</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001238821</rptOwnerCik>
            <rptOwnerName>GOODLATTE MARYELLEN F</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>PO BOX 2887</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ROANOKE</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>24001</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>2015-05-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>38.545</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>21.62</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14106.864</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares purchased pursuant to the Restricted Stock Plan for Outside Directors of RGC Resources, Inc.</footnote>
        <footnote id="F2">Includes 77.128 restricted shares purchased through dividends reinvested in the Restricted Stock Plan for Outside Directors of RGC Resources, Inc. and 47.355 shares purchased through dividends reinvested in the Dividend Reinvestment and Stock Purchase Plan for RGC Resources, Inc. Amended to adjust transaction price and share count of unrestricted shares purchased through dividend reinvestment.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Maryellen F. Goodlatte by Howard T. Lyon, POA dated 03/25/2002</signatureName>
        <signatureDate>2015-05-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
