map()

Description

Re-maps a number from one range to another. That is, a value of fromLow would get mapped to toLow, a value of fromHigh to toHigh, values in-between to values in-between, etc.

Does not constrain values to within the range, because out-of-range values are sometimes intended and useful. The constrain() function may be used either before or after this function, if limits to the ranges are desired.

Note that the "lower bounds" of either range may be larger or smaller than the "upper bounds" so the map() function may be used to reverse a range of numbers, for example

y = map(x, 1, 50, 50, 1);

The function also handles negative numbers well, so that this example

y = map(x, 1, 50, 50, -100);

is also valid and works well.

The map() function uses integer math so will not generate fractions, when the math might indicate that it should do so. Fractional remainders are truncated, and are not rounded or averaged.

Syntax

map(value, fromLow, fromHigh, toLow, toHigh)

Parameter Values

  • value: the number to map.
  • fromLow: the lower bound of the value's current range.
  • fromHigh: the upper bound of the value's current range.
  • toLow: the lower bound of the value's target range.
  • toHigh: the upper bound of the value's target range.

Return Values

  • The mapped value.

Example Code

/* Map an analog value to 8 bits (0 to 255) */ void setup() { pinMode(9, OUTPUT); // sets the pin as output } void loop() { int val = analogRead(0); val = map(val, 0, 1023, 0, 255); analogWrite(9, val); }

Appendix

For the mathematically inclined, here's the whole function

long map(long x, long in_min, long in_max, long out_min, long out_max) { return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min; }

Notes & Warnings

  • As previously mentioned, the map() function uses integer math. So fractions might get suppressed due to this. For example, fractions like 3/2, 4/3, 5/4 will all be returned as 1 from the map() function, despite their different actual values. So if your project requires precise calculations (e.g. voltage accurate to 3 decimal places), please consider avoiding map() and implementing the calculations manually in your code yourself.
  • The map() function returns an integer number. If you want to get the float number, you need to put the below custom function in your sketch and use it:
float floatMap(float x, float in_min, float in_max, float out_min, float out_max) { return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min; }
  • Or
double doubleMap(double x, double in_min, double in_max, double out_min, double out_max) { return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min; }

See Also

ARDUINO BUY RECOMMENDATION

Arduino UNO R3
Arduino Starter Kit
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