The Bra Size Calculator is a free tool that helps you calculate bra size using the formula Band from underbust; cup from the bust-minus-underbust difference. Enter your values above and press Calculate to get band size, cup difference instantly, with a full step-by-step breakdown.
What is the Bra Size Calculator?
The bra size calculator is a free online tool that helps you calculate bra size quickly and accurately. It applies the standard formula Band from underbust; cup from the bust-minus-underbust difference to the values you enter and, when you press Calculate, displays the result together with a clear, step-by-step explanation of how the answer was reached.
Also known as: bra calculator, bra size calculator in inches.
How to use the Bra Size Calculator
- Measure snugly under the bust.
- Measure around the fullest part.
- See an estimated size.
Formula used
The bra size calculator is based on this formula:
Band from underbust; cup from the bust-minus-underbust differenceEach term in the formula corresponds to one of the inputs explained below. The calculator performs the arithmetic for you and shows every step so you can check the working by hand if you wish.
Worked example
Suppose you enter underbust 75, bust 90. The calculator works as follows:
| Inputs | underbust 75, bust 90 |
|---|---|
| Working | difference 15 cm |
| Result | estimated band and cup |
Step-by-step calculation
- Apply the formula:
Band from underbust; cup from the bust-minus-underbust difference - Substitute your values: difference 15 cm
- Read the result: estimated band and cup
Inputs explained
- Underbust measurement (cm) — the underbust measurement used in the calculation.
- Bust measurement (cm) — the bust measurement used in the calculation.
Understanding your result
- Band size — the calculated band size.
- Cup difference — the calculated cup difference in cm.
Benefits and practical uses
The bra size calculator saves time and removes the risk of manual errors when you need to calculate bra size. It is useful for students, professionals and anyone who wants a fast, dependable answer. Results update the moment you press Calculate, work on any device, and can be copied or shared in a single click — and because the maths runs in your browser, your figures stay completely private.
Tips for an accurate result
- Keep all related inputs in the same units.
- Use the worked example above to confirm you are entering values in the right places.
- Review the assumptions below so the result fits your situation.
- Press Reset to clear everything and try a different scenario.
Common mistakes to avoid
- Entering values in the wrong unit (mismatched units give wrong answers).
- Leaving a required field empty — the calculator will ask you to fill it in.
- Treating the result as a diagnosis instead of a general guide.
Assumptions and limitations
- Measurements in centimetres; estimate only.
Frequently asked questions
Why do sizes vary by brand?
Sizing standards differ between brands and countries, so always try before buying.
How do I use the Bra Size Calculator?
Enter your values in the fields, then press the Calculate button to see the result. Use Reset to clear the form and start again. Nothing is calculated until you click Calculate.
What formula does the Bra Size Calculator use?
It uses the standard formula: Band from underbust; cup from the bust-minus-underbust difference. The full step-by-step working is shown with every result so you can verify it.
What information do I need to use the bra size calculator?
You need: underbust measurement, bust measurement. Sensible example values are pre-filled so you can see how it works.
Is the Bra Size Calculator free to use?
Yes. Every DigiToolkit calculator is completely free, with no sign-up, no login and no usage limits.
Does the Bra Size Calculator work on mobile phones?
Yes. The calculator is mobile-first and works on phones, tablets and computers in any modern browser.
Do I need to install an app?
No. The bra size calculator runs directly in your web browser — there is nothing to download or install.
Is my data private when I use this calculator?
Yes. All calculations run inside your browser. The numbers you enter are never uploaded to a server or shared with anyone.
How accurate is the Bra Size Calculator?
It uses the generally accepted formula for bra size and computes to several decimal places. Results are accurate for the assumptions listed on this page.
Can I copy or share my result?
Yes. After calculating, use the Copy button to copy the result, or Share to copy the page link.
Why is nothing showing until I press Calculate?
By design, the calculator only computes when you press Calculate, so you can finish entering all your values first. Press Reset any time to clear everything.
What units does the Bra Size Calculator use?
It works with cm. Keep your inputs in consistent units for an accurate result.