👙 Premium Lingerie Fitting & Measurement Tool

Bra Size Calculator & International Fit Guide

Find your true bra size in seconds using accurate underbust and bust measurements. Includes sister size recommendations, cup volume calculations, and full US, UK, EU, FR, AU, JP conversion charts.

Measurement Units:

⚙️ Body Measurements

30.0 in

Measure snug directly under your bust around your ribcage.

36.0 in

Measure loosely around the fullest part of your chest.

Round

💡 Round Profile: Equal fullness throughout. Fits almost all bra styles including t-shirt, plunge, and balcony bras.

Sister Sizes (Equivalent Cup Volume)

Sister sizes have the exact same cup volume but different band tightness. If your current band is too loose or too tight, try a sister size!

Looser Band 36B
↔
Tighter Band 32D

📊 Live International Size Results Real-time calculations

US / Canada Size
34C
US Standard
UK / Australia Size
34C
UK / AU Standard
EU / FR / JP Size
75C
EU / FR / JP Metric
Sister Size Alternative
36B / 32D
Same Cup Volume
Cup Volume: Medium (C Cup)
Bust - Underbust Diff: 6.0 in (15 cm)
Recommended Cup: C Cup
Anatomical Bra Visualizer
34C Fit Projection
Quick Presets:
34C
Elastic Underbust Band Anatomical Cup Projection

📖 International Bra Size & Cup Conversion Chart

Underbust (in / cm) US / CA Band UK / AU Band EU / JP Band Difference Cup Size
⚡

Auto Screen Calibration

OnlineRulerAI auto-detects your screen PPI database (250+ devices) to display 100% 1:1 real-world dimensions instantly.

💳

Credit Card & Coin Fit

Match any standard credit card (85.60 mm), bank card, or coin against your display for pinpoint physical accuracy.

🎯

Visual Caliper & Guidelines

Drop reference guidelines, track cursor crosshairs, or drag rulers across screen edges in inches, cm, mm, and px.

Free Online Ruler — Measure in Inches, cm & mm at Actual Size

Free online ruler calibrated to actual size in inches, cm, and mm without downloads. Features auto screen detection, credit card calibration, protractor, and visual calipers.

Calibrate for 100% Physical Accuracy

Click Calibrate to auto-detect your screen or match a physical credit card, banknote, or monitor diagonal.

  • 1. Device Database: Auto-detect screen PPI database (250+ devices).
  • 2. Screen Diagonal: Calculate exact PPI from monitor diagonal in inches.
  • 3. Credit Card: Match physical credit card (85.60 mm) to on-screen slider.
  • 4. Banknote & Object: Compare physical banknote or coin against screen.

Select Your Measurement Unit

Switch between Centimeters (cm), Millimeters (mm), Inches (inch), Pixels (px), Points (pt), Picas, Feet, and Yards.

Place & Measure Objects

Place objects along screen edge rulers, drag visual caliper, or click Guidelines/Crosshair to measure in real time.

❓ Frequently Asked Questions (FAQ)

Click any question below to expand the detailed answer.

Q1. Can I use my phone as a ruler?
Yes! OnlineRulerAI turns any smartphone (iPhone, Android, Samsung, Pixel) into a 1:1 actual size digital ruler. You can calibrate your mobile display using a standard credit card (85.60 mm) or auto-detect your device model to measure physical objects directly on your screen.
Q2. Is there a ruler online?
Yes, OnlineRulerAI provides a free online ruler calibrated to actual real-world physical dimensions. It displays 12 inch, 30 cm, and millimeter scale lines on your monitor, tablet, or mobile phone screen without downloading any app.
Q3. How to identify 1 inch?
One inch equals exactly 2.54 centimeters or 25.4 millimeters. On an actual size online ruler, 1 inch is demarcated by the longest tick mark labeled with a '1″' symbol.
Q4. How to measure cm online?
Select the 'cm' unit button on OnlineRulerAI. Place your physical object flat against your screen aligned with the zero line (0 cm), and read the corresponding major mark.
Q5. Can a smartphone measure?
Yes, via camera AR apps or directly on screen using OnlineRulerAI browser tools for small items up to 15 cm with millimeter precision.
Q6. Can I use my camera as a ruler?
Yes! Camera ruler applications use AR camera alignment to measure room dimensions, furniture, and larger physical items in real-time.
Q7. Can we measure online?
Absolutely. You can measure physical items directly on your computer or mobile screen using OnlineRulerAI's free web tools.
Q8. How to read a ruler online?
Align one end of your object with the '0' mark. In cm mode: numbered tick marks are centimeters; smallest ticks are millimeters. In inch mode: numbered ticks are full inches.
Q9. How to view or add a ruler in Word Online?
In Microsoft Word Online, click on the 'View' tab in the top ribbon and check the 'Ruler' box.
Q10. How to show a ruler in PowerPoint Online?
In Microsoft PowerPoint Online, navigate to the 'View' tab and check the 'Ruler' box.
Q11. How to use an online ruler?
Open OnlineRulerAI in your browser, click 'Calibrate' to adjust your screen PPI with a credit card or device model, and lay your object flat on the screen to measure.

How to Measure Your Bra Size Accurately at Home

Over 80% of women wear the incorrect bra size, often wearing a band that is too loose and cups that are too small. An ill-fitting bra can cause back pain, shoulder strain, and discomfort throughout the day. Our Bra Size Calculator uses professional bra fitting algorithms to find your ideal band and cup combination.

Two Steps to Find Your True Bra Size

1. Measure Your Underbust (Band Size)

Wrap a soft tape measure directly under your bust around your ribcage. Keep the tape parallel to the floor and pull it snug. This measurement determines your band size.

2. Measure Your Bust (Cup Size)

Wrap the tape measure around the fullest part of your bust (usually across the nipples). Keep the tape level and loose without compressing the tissue.

3. Calculate Cup Difference

Subtract your underbust measurement from your bust measurement. Each 1-inch difference represents one cup size (1" = A cup, 2" = B cup, 3" = C cup, 4" = D cup, 5" = DD/E cup).

Understanding Bra Sister Sizes

Sister sizes are bra sizes that hold the same cup volume even though the band size changes. For example, a 34C holds the exact same amount of breast tissue as a 32D (tighter band) and a 36B (looser band).

Frequently Asked Questions (FAQ)

How should a bra fit properly around the band?

The band provides 80% of your bra's support. It should rest firmly and horizontally across your back without riding up. You should be able to slide no more than two fingers under the band.

Why does my cup size change when I change band size?

Cup sizes are proportional to band sizes, not absolute volumes. A 36D cup is significantly larger in volume than a 32D cup because cup depth is calculated relative to ribcage circumference.

Calibrate

Choose a method for 100% physical accuracy.

Viewport Resolution -- x --
Device Pixel Ratio 1.0
250+ Models
PPI

Guide

Master shortcut keys for fast measuring.

Drawing Tools

Guidelines [G]

Click anywhere on screen to drop persistent horizontal or vertical alignment lines labeled with exact physical distances.

Crosshair [X]

Full-screen dual-axis crosshairs following your cursor with real-time X and Y coordinate measurements.

Keyboard Shortcuts

Toggle Guidelines Tool G
Toggle Full-Screen Crosshair X
Clear All Guidelines & Overlays Esc
Switch Units (cm, mm, inch, px)
1 (cm) 2 (mm) 3 (inch) 4 (px)
Toggle Full Dark / Full Light Theme D
Toggle Caliper Box C
Open Calibration Dialog K
Toggle Fullscreen Mode F