C6H4O4

The molecular formula C6H4O4 may refer to:
 * Coumalic acid
 * Dihydroxybenzoquinones
 * 2,3-Dihydroxy-1,4-benzoquinone
 * 2,5-Dihydroxy-1,4-benzoquinone
 * 2,6-Dihydroxy-1,4-benzoquinone
 * 3,4-Dihydroxy-1,2-benzoquinone
 * 3,5-Dihydroxy-1,2-benzoquinone
 * 3,6-Dihydroxy-1,2-benzoquinone
 * 4,5-Dihydroxy-1,2-benzoquinone
 * 5-Carboxyfurfuraldehyde
 * 2-Furylglyoxylic acid
 * 3-Furylglyoxylic acid