The California-based company has moved into flash-storage technology as disk-drive sales dwindle.
The SanDisk acquisition was closed in May, bringing in more customers and a broader portfolio of hard-drive and flash-storage products.
The group now sees revenue for the three months to September to reach between US$4.45bn and US$4.55bn, compared with the previous forecast of US$4.4bn to US$4.5bn.
An improved product mix and pricing is expected to help expand adjusted gross margins.
Western Digital expects to earn between US$1 and US$1.05 a share, compared with its earlier estimates of between US$0.85 and US$0.90 a share.
Full results will be reported late October.
Last year the group announced a US$19bn cash-and-stock deal to buy SanDisk, where sales of enterprise solutions and removable products have been rising.
In July, Western Digital posted a quarterly loss on costs associated with the integration of SanDisk, but results were nonetheless higher than expected.
SanDisk pushed up total sales 9.5% during the quarter.
Shares in Western Digital rose 5.5% to US$50.15 in premarket trading.