# How do I convert a Float64 number to Int64?

**URL:** <https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244>\
**Category:** General Usage\
**Created:** [October 13, 2024, 6:27am UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244 "2024-10-13T06:27:00Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![hack3rcon](https://avatars.discourse-cdn.com/v4/letter/h/96bed5/32.png) [@hack3rcon](https://discourse.julialang.org/u/hack3rcon)\
**Post date:** [October 13, 2024, 6:27am UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244/1 "2024-10-13T06:27:00Z")

</div>

Hello,  
Is it possible to convert a Float64 number directly to Int64?

```julia
julia> number=6.5
6.5

julia> typeof(num)
Float64

julia> Int(number)
ERROR: InexactError: Int64(6.5)
Stacktrace:
 [1] Int64(x::Float64)
   @ Base ./float.jl:912
 [2] top-level scope
   @ REPL[22]:1

```

Thank you.

---

<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [October 13, 2024, 6:36am UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244/2 "2024-10-13T06:36:39Z")

</div>

If the number doesn’t have an integer value (like 6.0), you must _round_. Then you must decide what sort of rounding you want:

```julia
round(Int, x) # closest int
floor(Int, x) # downwards 
ceil(Int, x) # upwards

```

There are some more variations, like `trunc`.

---

<div class="post-metadata">

**Author:** ![Benny](https://avatars.discourse-cdn.com/v4/letter/b/49beb7/32.png) [@Benny](https://discourse.julialang.org/u/Benny)\
**Post date:** [October 13, 2024, 6:44am UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244/3 "2024-10-13T06:44:07Z")

</div>

A mostly useless but reversible alternative to semantic conversion: `reinterpret(Int64, x::Float64)`

---

<div class="post-metadata">

**Author:** ![hack3rcon](https://avatars.discourse-cdn.com/v4/letter/h/96bed5/32.png) [@hack3rcon](https://discourse.julialang.org/u/hack3rcon)\
**Post date:** [October 13, 2024, 6:53am UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244/4 "2024-10-13T06:53:23Z")

</div>

Hi,  
Thank you so much.

---

<div class="post-metadata">

**Author:** ![JeffreySarnoff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeffreysarnoff/32/1980_2.png) [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)\
**Post date:** [October 13, 2024, 7:04am UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244/5 "2024-10-13T07:04:35Z")

</div>

Some Float64 numbers have Integer values (e.g. -4.0, 0.0, 1.0, 64.0). They convert to Int64 directly.

```julia
julia> Int64(-4.0), Int64(0.0), Int64(64.0)
(-4, 0, 64)

```

Some Float64 values are too large (positive or negative) to fit in an Int64. Many Float64 values exceed the magnitude of largest Int64 (`typemax(Int64)`).

```julia

julia> Int64(Float64(typemax(Int64)/2))
4611686018427387904

julia> Int64(3*Float64(typemax(Int64)/2))
ERROR: InexactError: Int64(1.3835058055282164e19)
Stacktrace:
 [1] Int64(x::Float64)
   @ Base .\float.jl:994
 [2] top-level scope
   @ REPL[26]:1

```

To convert Float64 values that are small enough for Int64s, you must set the fractional part of the Float64 to 0  
(e.g. 3.14 → 3.0 or 4.0, 5.5 → 5.0 or 6.0). There are different rounding modes you may choose to use for this purpose.

```julia
pos = 2.5
neg = -2.5
round(pos, RoundUp), round(neg, RoundUp)
# (3.0, -2.0)
round(pos, RoundDown), round(neg, RoundDown)
# (2.0, -3.0)
round(pos, RoundToZero), round(neg, RoundToZero)
# (2.0, -2.0)
round(pos, RoundFromZero), round(neg, RoundFromZero)
# (3.0, -3.0)

# RoundNearest resolves values halfway between (x.5)
# by choosing the nearest even
round(pos, RoundNearest), round(neg, RoundNearest)
# (2.0, -2.0)
# RoundNearestTiesAway and RoundNearestTiesUp also work round(pos, RoundNearestTiesAway), round(neg, RoundNearestTiesAway)
# (3.0, -3.0)
round(3.5, RoundNearestTiesAway), round(-3.5 RoundNearestTiesAway)
# (4.0, -4.0)

round(pos, RoundNearestTiesUp), round(neg, RoundNearestTiesUp)
# (3.0, -2.0)

```

Whichever rounding mode you use, once the fractional part is rounded away, it will convert to an Int64 as long as it fits.

```julia
Int64(round(pi, RoundUp)), Int64(round(-pi, RoundNearest))
(4, -3)

```

Julia lets you combine the two steps.

```julia
round(Int64, pi, RoundUp), round(Int64, -pi, RoundNearest)
(4, -3)

```

fyi `trunc(Int64, x)` works like Int64(round(x, RoundToZero)).

---

<div class="post-metadata">

**Author:** ![hack3rcon](https://avatars.discourse-cdn.com/v4/letter/h/96bed5/32.png) [@hack3rcon](https://discourse.julialang.org/u/hack3rcon)\
**Post date:** [October 13, 2024, 9:14am UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244/6 "2024-10-13T09:14:53Z")

</div>

Hi,  
Thank you so much for these great examples.

---

<div class="post-metadata">

**Author:** ![j\_verzani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/j_verzani/32/8551_2.png) [@j\_verzani](https://discourse.julialang.org/u/j_verzani)\
**Post date:** [October 13, 2024, 3:01pm UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244/7 "2024-10-13T15:01:26Z")

</div>

Not so useless 🙂 We use it in `Roots,jl` to make a more robust Bisection method ([Roots.jl/src/Bracketing/bisection.jl at master · JuliaMath/Roots.jl · GitHub](https://github.com/JuliaMath/Roots.jl/blob/master/src/Bracketing/bisection.jl#L130)).

---

<div class="post-metadata">

**Author:** ![Palli](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/palli/32/3380_2.png) [@Palli](https://discourse.julialang.org/u/Palli)\
**Post date:** [October 13, 2024, 7:19pm UTC](https://discourse.julialang.org/t/how-do-i-convert-a-float64-number-to-int64/121244/8 "2024-10-13T19:19:13Z")

</div>

I question that you need to convert to integers ever.

You can’t do it in general, e.g.

```julia
julia> typemax(Int64) # this 19-digit number is the max.
922337203685477580

julia> Int64(999_999_999_999_999.0) # Float64 has 15 significant digits, and number up to this size should be safe:
999999999999999

julia> Int64(9_999_999_999_999_9999.0) # This is seemingly the first number that fails:
10000000000000000

julia> Int64(round(999_999_999_999_9993.4)) # Fail
9999999999999994

```

Float64, and even Float32 (but not Float16) allow way larger integers than can fit into Int64:

```julia
julia> Int64(round(floatmax(Float32)))
ERROR: InexactError: Int64(3.4028235e38)

julia> BigInt(round(floatmax(Float32)))
340282346638528859811704183484516925440

```