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Sig Fig Subtraction Calculator

Use this free sig fig subtraction calculator to subtract two numbers and automatically round the result to the correct precision using the subtraction sig fig rule (fewest decimal places).

Enter Values

First Number

The number to subtract from

Second Number

The number to subtract

Result

Enter values above and click Calculate to see your result.

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Formula

Round the difference to the least precise decimal place among the inputs

When subtracting, the result is rounded to the same decimal place as the measurement with the fewest decimal places, following the same rule as addition.

Worked Example

Subtract 45.876 - 0.34 Step 1: 45.876 has 3 decimal places. 0.34 has 2 decimal places. Step 2: The limiting factor is 2 decimal places (from 0.34). Step 3: 45.876 - 0.34 = 45.536 Step 4: Round to 2 decimal places: 45.54 Result: 45.54

Sig Fig Rule for Subtraction

Subtraction follows the same significant figures rule as addition. The result is rounded to the decimal place of the measurement with the fewest decimal places. This is especially important in subtraction because subtracting two close values can dramatically reduce the number of meaningful sig figs.

Subtraction uses the decimal places rule, identical to addition
Subtracting similar values causes "catastrophic cancellation," which can reduce sig figs significantly
Example: 5.67 - 5.64 = 0.03, which has only 1 sig fig even though both inputs had 3
This loss of precision is a real measurement concern, not just an arithmetic technicality

Understanding precision loss in subtraction is critical in experimental science. When two measurements are nearly equal, their difference has much less precision than either individual measurement.

You can also calculate changes using our Sig Fig Addition Calculator, Sig Fig Rules Calculator or Sig Fig Division Calculator.

Frequently Asked Questions

Why can subtraction reduce sig figs so much?

When you subtract two nearly equal numbers, the leading significant digits cancel out, leaving fewer meaningful digits. For example, 23.456 - 23.441 = 0.015, which has only 2 sig figs despite both inputs having 5.

Is this the same rule as addition?

Yes, subtraction and addition use the identical rule: round the result to the same decimal place as the input with the fewest decimal places.

What is catastrophic cancellation?

It is when subtracting two nearly equal numbers causes a dramatic loss of significant figures. Scientists try to avoid experimental designs that rely on small differences between large measurements for this reason.

How do I avoid precision loss in subtraction?

Use instruments with more decimal places, redesign the experiment to measure the difference directly rather than subtracting two large measurements, or use algebraic rearrangements that avoid subtracting similar values.

Does this apply to negative results?

Yes. The rule applies regardless of whether the result is positive or negative. The decimal place of each input still determines the precision of the answer.

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