I have a iphone charger but it won't charge to my ipad

First, make sure that the USB port is powerful enough to charge your iPad, iPads need more power than iPhones to charge. If that doesn’t work then test the cable with other devices. (iPads need 2.1 amps, and iPhones need 1)

The majority of iPad models require a Power Adapter rated at 10-12W (i.e., 2.0-2.4A @5V) or greater. Most iPhone Power Adapters are only rated at 5W (1A @5V) - this being inadequate to charge an iPad.