I sold land for $100,000 how much tax do I have to pay

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Q. I sold land for $100,000 how much tax do I have to pay.

A. Simple answer: 15% of the capital gain (profit) on the sale. 

But taxes aren't simple.  Depending on how much other income you have, it could be more or less.  For low income people, some of their long term (property owned over one year) capital gain is taxed a 0%.  For high income people, it's as much as 23.8%. 

Capital gains tax explained: https://www.nerdwallet.com/article/taxes/capital-gains-tax-rates

You can try this tool https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1. Enter your regular income first to see the regular tax. Then add the sale to see the effect.
Enter the difference between the sale price and what you paid for it originally as Gains/Losses  (long term capital gain [LTCG]).