SuperCalX logoSuperCalX

Bra Size Calculator

Estimate your bra size based on band and bust measurements.
What This Calculator Helps You Do
Use the inputs below to test scenarios, compare outcomes, and interpret the result before acting on it.

Bra Size Calculator is designed to give you a fast answer, but it also provides supporting context such as formulas, worked examples, FAQs, and charts so the result is easier to validate.

For the best result, use realistic input values, review the assumptions in the explanation panels, and compare multiple scenarios if you are planning a decision based on the output.

Calculator
Enter your values
Analysis
Interpretation of the current calculator output

Enter values to see detailed analysis and insights.

How to Use

Step-by-step instructions
  1. 1Measure your underbust (snug, around ribcage).
  2. 2Measure your bust (fullest part).
  3. 3Enter the measurements in inches.
  4. 4The calculator will estimate your US size.

US Standard Sizing

Calculates band size by adding 4-5 inches to the underbust measurement (standard US method), then determines cup size by the difference between bust and band.
Cup = Bust - Band

Variables:

BandUnderbust + 4/5 inches
Cup1" diff = A, 2" = B, etc.

Example

30" Underbust, 35" Bust

Inputs:

Underbust:30 inches
Bust:35 inches

Steps:

  1. 1.Band = 30 + 4 = 34
  2. 2.Diff = 35 - 34 = 1 inch
  3. 3.1 inch = A Cup
Result:
34A

Frequently Asked Questions

Why +4 inches?

This is a traditional sizing method used by many US brands. Some modern fitting methods use the underbust measurement directly as the band size (e.g., 30" = 30 Band), which would result in a larger cup letter (e.g., 30DD).

What are sister sizes?

Sister sizes are bra sizes that have the same cup volume but different band lengths. If a bra fits in the cup but is too loose/tight in the band, try a sister size.
In-depth guideBrowse Everyday Life calculators
Bra Size Calculator Guide
Detailed usage notes, assumptions, mistakes to avoid, and related tools.

Bra Size Calculator helps turn the available inputs into a result that is easier to check, compare, and explain. Estimate your bra size based on band and bust measurements.

Use this page together with 0-60 Calculator when your question touches related assumptions in the same everyday life workflow. For a nearby workflow, open 0-60 Calculator.

Formula And Variables
How the calculator turns inputs into an answer.

US Standard Sizing is the main method behind this calculator. The equation is Cup = Bust - Band, and the calculator applies it consistently as you change the inputs.

The most important variables are: Band is underbust + 4/5 inches, Cup is 1" diff = a, 2" = b, etc.. Check those values first if the output looks higher or lower than expected.

How To Use The Result
What to compare before acting on the output.

The worked example on this page uses Underbust = 30 inches, Bust = 35 inches and produces 34A. Use that example as a quick check for the calculation flow before entering your own values.

For practical use, read the bra size calculator result as a decision-support number. It is strongest when you compare two or more scenarios using the same units and assumptions.

Data Visualization And Analysis
Different chart views answer different questions about the same calculator output.

Best ways to read the charts

Use a bar chart when you need to compare separate result components, a line or area chart when the output changes across steps or time, and a pie-style distribution when every value is part of one total.

When the page shows multiple chart tabs, start with the overview, then check the ranking view to see which value drives the result most strongly.

What the analysis should tell you

Compare the average, range, highest value, lowest value, and dominant contributor before making a conclusion from the main number alone.

If one value contributes most of the total, test that assumption first. If values are spread evenly, the result is usually driven by the full input set rather than a single outlier.

Common Mistakes
  • Do not mix units unless the calculator explicitly converts them for you.
  • Avoid copying a result without checking whether the inputs describe the same time period, measurement system, or scenario.
  • If the answer looks surprising, change one input at a time so you can identify which assumption is driving the output.
When The Result May Be Inaccurate

The result can be inaccurate if inputs use mixed units, rounded source data, outdated rates, or assumptions that do not match the situation being modeled.

Run a second scenario with conservative inputs when the output will affect a purchase, project, health decision, academic answer, or financial plan.

Related Calculators
Continue through the same topic cluster with crawlable internal links.
0-60 Calculator

Estimate a car

Age Calculator

Calculate your exact age in years, months, and days.

Clothing Size Converter

Convert clothing sizes between US, UK, EU, and International standards.

Date Calculator

Add or subtract time from a date, or calculate the days between two dates.

Electricity Bill Calculator

Estimate your monthly electricity bill based on meter readings.

Fuel Cost Calculator

Calculate the fuel cost for a trip.

Additional Questions

How accurate is Bra Size Calculator?

Bra Size Calculator is accurate for the formula and inputs shown on the page. Real-world accuracy depends on whether the values you enter are complete, current, and measured in the expected units.

What should I check before using the bra size calculator result?

Check the input units, review the formula section, compare the worked example, and run at least one alternate scenario if the result will support a decision.