How to convert token to full token without having any rounding errors.


TypeError: num.isZero is not a function at BN.divmod (node_modules/number-to-bn/node_modules/bn.js/lib/bn.js:2329:17) at BN.div (node_modules/number-to-bn/node_modules/bn.js/lib/bn.js:2425:17) at Promise.all.then () at at process._tickCallback (internal/process/next_tick.js:182:7)

        bal=6221221111111110001/ (10**(18))

It also has some precision errors.

Any help is appreciated.

  • The error-message implies that you are using web3.utils.toBN, not web3.toBigNumber. Please clarify your question. Commented Dec 18, 2020 at 8:27
  • And the expression bal=balance/ (10**(18)) means nothing to us when we have no idea what bal and balance are. Please clarify that as well. Commented Dec 18, 2020 at 8:28
  • Also 12345 / 10 ** 15 is a value smaller than 1. If you plan to send it to a contract function, then you'll need to convert it to an integer, which means it's going to be a simple 0. So what exactly are you trying to do here? Also, how on earth is that related to bal=balance/ (10**(18)) at the end of the question? Commented Dec 18, 2020 at 8:34
  • @goodvibration Sorry for the typo.Updated the question Commented Dec 18, 2020 at 8:54
  • What do you mean "without having any rounding errors"? Function web3.utils.toBN.div gives you the integer division, do you want a regular division? You do realize that you will not be able to send the result to a contract function, right? In other words, it will be useful only on your offchain (Javascript) side. Commented Dec 18, 2020 at 8:56

1 Answer 1


First of all, regarding the specific error in your question, change this:


To this:


Or to this:


Second, since class BN supports only integer-arithmetic, the result of your computation is 6.

in order to perform non-integer computation, you will need to use class Decimal instead:

const Decimal = require('decimal.js');
const str = Decimal(6221221111111110001).div(Decimal(10).pow(18)).toFixed();

Or simply:

const str = Decimal('6221221111111110001e-18').toFixed();

Note that you will not be able to send this result to a contract function.

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