Romans 12:3:

For I say, through the grace given unto me, to every man that is among you, not to think of himself more highly than he ought to think; but to think soberly, according as God hath dealt to every man the measure of faith.

Notes on Romans 12:3:

God has given you faith as a gift.  It is not something that you work up; it is something that you already have.   Don’t let the devil lie to you that you don’t have any faith.  This verse proves that you do!  The word measure is the Greek word metron, which indicates a measure designed to contain a fixed amount of something.  Thus, God gives everyone the same measure of faith, though some people do more with it than others.  Because Jesus had to be made a REAL MAN like you, God gave you and Jesus the same measure of faith, though it’s safe to say that He made the greatest use of it of all people who have ever lived.  He showed you what is possible for YOU walking as a person who exercises faith.  What HIS faith did, YOUR faith can do, because it’s the same faith.  Thus, it’s not necessary to ask God for “the God-kind of faith” because you already have it!

You already have the ability to believe but you need to hear the Word of God to know what to believe.

See also:

Notes on Matthew 21:18-22
Notes on Romans 10:17
You Have Faith
Faith Is a Gift from God
Who You Are and What You Have
You’re Not an Exception
Peace in a Storm
What Mark 11:22 Really Means
The Insecure Preacher
Would God Heal an Unbeliever?
Does Mark 11:23 Work for Unbelievers?
What Are the Differences Between the Gift of Faith, the Gifts of Healings, and the Working of Miracles?
How Can Faith COME by Hearing When We Already HAVE the Measure of Faith?
How Can My Faith GROW If I Already Have the Fixed Measure of Faith?
Is Faith a Force?
If God Gives Everyone Faith, How Can Anyone Ever Be in Unbelief?  Isn’t Unbelief the Absence of Faith?
How Can Faith Be Both a Fruit of the Spirit and a Gift of the Spirit?
Does Faith Come from Your Spirit, Your Mind or Somewhere Else?
Objection: Many Who Are “in Faith” for Their Healing Die Anyway
Objection: We Cannot Expect to Heal as Jesus Did Because We Are Not the Son of God
Objection: Mark 16:18 Does Not Say, “They Shall Recover IF They Have Enough Faith,” Yet Faith Healers Blame the Sick for Not Believing
Objection: Teaching Grace Gives People a License to Sin
Objection: Faith Is a Gift from God (Ephesians 2:8), So You Can’t Believe Unless God Gives You the Faith to Do It
Objection: Faith Is a Gift from God, Not Something You Work Up Yourself
Objection: Faith Teaching Negates Compassion on the Sufferer; We're Taught Instead to Blame the Person for Not Having Enough Faith
Objection: Only Some People Have the “Gift of Faith” to Believe for Healing