---
title: "How to use operators and functions in equations"
description: "Type operators and functions into a popup equation, such as rounding and percentages. Use the same syntax in Custom and Calculator popups."
seo:
  title: "Use operators and functions"
sidebar:
  label: "Operators and functions"
---

Type an expression like `round(({part} / {total}) * 100)` into an equation, and each feature shows the computed result — a rounded percentage here, a different one on the next feature. The equation editor has toolbar buttons for five operators, but it's a free-text field, so you can type any supported operator or function directly; the only rule is that the expression must work out to a single number. Equations work with numbers only: they cannot show text.

This applies to both places equations are used: the equation extension in a Custom popup, and Step 3 of a Calculator popup. The syntax is identical. For the full list of operators, functions, and formatting methods, see [Calculator formula syntax](/docs/configuring-popups/calculator-formula-reference).

## Before you start

- You need a Custom popup with the equation extension, or a Calculator popup. See [How to add a calculated value to a custom popup](/docs/configuring-popups/add-equations-to-popup) or [How to build a calculator popup](/docs/configuring-popups/build-a-calculator-popup).
- The attributes you reference (`{field_name}`) must exist on the layer and hold numbers. Non-numeric attributes can be referenced but won't compute usefully.
- Equations evaluate per feature. Layer-wide aggregations (`sum`, `avg`, `count`) aren't available here — those live in the [Query](/docs/map-extensions/set-up-the-query-tool) and [Proximity Analysis](/docs/map-extensions/set-up-proximity-analysis) tools.

## Enter an operator or function

For the five common operators — `+`, `-`, `*`, `/`, and parentheses — click the buttons in the modal's `Operators` group, or type them. Other operators and all functions are typed directly:

- **Operators you type:** modulo `%`, exponentiation `^`, unary negative (`-{field}`), factorial `!`.
- **Functions you type:** `round(...)`, `floor(...)`, `min(...)`, and the rest. Names are case-sensitive — `round`, not `Round`. Put parentheses around the argument: `round({population} / {area})`.

Watch the `Preview (with sample values)` panel as you type. It calculates the expression with the values of one sample feature and shows `= <number>`. If it shows a message in red, check the formula before saving. See [If the preview shows an error](#if-the-preview-shows-an-error).

## Basic arithmetic

The everyday operators. Parentheses force the order you want; without them, `^` runs before `*` `/` `%`, which run before `+` `-`.

In the tables below, the last column is the value to type in `Decimal Places` for that formula. It is not set by the formula. The default is `2`.

| Goal | Formula | Set Decimal Places to |
| --- | --- | ---: |
| Add two attributes | `{male} + {female}` | `0` |
| Subtract one from another | `{total} - {male}` | `0` |
| Multiply | `{rate} * {total}` | `2` |
| Divide | `{total} / {households}` | `2` |
| Group before dividing | `({male} + {female}) / {households}` | `2` |
| Negative of a value | `-{change}` | `0` |
| Remainder after dividing | `{total} % {per_box}` | `0` |
| Raise to a power | `{side} ^ 2` | `0` |

## Rounding and numeric functions

Functions wrap an expression and transform its result. Rounding functions are the most common — note that `Decimal Places` only controls how the final number is *displayed*, whereas `round`, `floor`, and `ceil` change the value itself.

| Goal | Formula | Set Decimal Places to |
| --- | --- | ---: |
| Round to the nearest whole number | `round({total} / {households})` | `0` |
| Always round down | `floor({total} / {households})` | `0` |
| Always round up | `ceil({total} / {households})` | `0` |
| Drop a negative sign | `abs({male} - {female})` | `0` |
| Smaller of two attributes | `min({this_year}, {last_year})` | `0` |
| Larger of two attributes | `max({this_year}, {last_year})` | `0` |

## Thousand separators and fixed decimals

Add a formatting method to the end of a formula to change how the result shows. `.toLocaleString()` adds thousand separators. `.toFixed(n)` shows exactly `n` decimals. You can use both, in either order. A formatting method replaces the `Decimal Places` setting.

| Goal | Formula | Result |
| --- | --- | --- |
| Whole number with thousand separators | `round({population} / {area}).toLocaleString()` | `12,508` |
| One decimal with thousand separators | `roundTo({population} / {area}, 1).toLocaleString()` | `12,508.3` |
| European number style | `round({population} / {area}).toLocaleString('de-DE')` | `12.508` |
| Exactly one decimal, no separators | `({part} / {total} * 100).toFixed(1)` | `45.7` |
| Exactly two decimals with thousand separators | `({population} / {area}).toFixed(2).toLocaleString()` | `12,508.28` |

`.toLocaleString()` shows up to 3 decimals, with no zeros at the end. To set the decimals, round inside the formula or add `.toFixed(n)`.

The locale code can also show the digits in another script, such as Thai (`.toLocaleString('th-TH-u-nu-thai')` gives `๑๒,๕๐๘`) or Arabic (`'ar-EG'`). For the locale codes and scripts, see [Locales and number scripts](/docs/configuring-popups/calculator-formula-reference#locales-and-number-scripts). For every rule, see [Format the result](/docs/configuring-popups/calculator-formula-reference#format-the-result).

## Real-world calculations

The kinds of formulas you'll actually choose — shares, ratios, differences, and averages.

| Goal | Formula | Set Decimal Places to |
| --- | --- | ---: |
| One attribute as a percentage of a total | `({part} / {total}) * 100` | `2` |
| Two attributes combined, as a share of a total | `(({a} + {b}) / {total}) * 100` | `2` |
| Rounded percentage | `round(({part} / {total}) * 100)` | `0` |
| Sum of two categories | `{widowed} + {divorced}` | `0` |
| Difference between two categories | `abs({category_a} - {category_b})` | `0` |
| Difference between two measures | `{measure_f} - {measure_m}` | `2` |
| Average of two measures | `({measure_a} + {measure_b}) / 2` | `2` |

## If the preview shows an error

The preview shows a message in red when the expression does not give a single number for the sample feature. Common causes:

- **`Result is not a number`** — a comparison or logical operator on its own. `{a} > {b}` and `{a} and {b}` give true or false, not a number. To use a comparison, wrap it in a conditional: `if({stock} > 0, {price}, 0)` returns a number.
- **`Result is not a number`** — text in the formula. An equation cannot show text. In `if({stock} > 0, {price}, 'Sold out')`, the popup shows the price when `stock` is above zero, and is blank for every other feature. The preview shows this message only when the sample feature takes the text branch. Both branches must be numbers. To show `Sold out`, use [conditional content](/docs/configuring-popups/add-conditional-content-to-popup).
- **`Syntax error`** — an unmatched parenthesis, or a function name spelled wrong (`Round` instead of `round`).
- **`Field not found: {name}`** — the layer has no attribute with that name. Check the spelling.
- **`Not a number: name`** — the sample feature has a text value for the attribute.
- **`Division by zero`** — the formula divides by zero for the sample feature.

Fix the formula until the preview shows `= <number>`, then save.

`No sample value for {name}` means that the sample feature has no value for the attribute. The formula can still work for other features. Click `Insert Equation`, save the popup, and check the result on the map. For every message, see [Preview messages](/docs/configuring-popups/calculator-formula-reference#preview-messages).

## Related

- [Calculator formula syntax](/docs/configuring-popups/calculator-formula-reference) — the full operator and function list.
- [How to add a calculated value to a custom popup](/docs/configuring-popups/add-equations-to-popup)
- [How to build a calculator popup](/docs/configuring-popups/build-a-calculator-popup)
- [How to add dynamic content to a custom popup](/docs/configuring-popups/add-dynamic-content-to-popup)