Method 1: string and a ruler
This is the best substitute and gives results as good as a proper tape.
What to use
Anything long, thin and non-stretchy: kitchen string, a shoelace, a phone charging cable, dental floss, a non-elastic ribbon. Avoid wool, elastic and anything that gives when you pull it.
How to do it
- Wrap the string around your ribcage directly under your bust, level all the way round, and pull it snug.
- Pinch the point where the end meets the rest of the string, or mark it with a pen.
- Lay the string straight against a ruler, a steel tape or a metre stick and read the length. With a 30 cm ruler, measure in sections and add them up.
- Repeat around the fullest part of your bust, this time letting the string rest on the skin without pulling in.
Enter the two numbers in the calculator, in inches or centimetres.
Method 2: paper as a ruler
If you have string but nothing to measure it against, standard paper works as a ruler. A sheet of A4 is 29.7 cm long and 21 cm wide, in every country that uses it.
- Three long edges of A4 are 89.1 cm.
- Fold a sheet in half along its length to mark 14.85 cm, and in half again for about 7.4 cm.
- Lay your marked string along the paper edge, counting whole lengths and estimating the remainder with the folds.
You can expect to be within a centimetre or so, which is close enough to find your band and narrow your cup to one of two sizes. Use the centimetre calculator for the result.
Method 3: read it from a bra you own
No string, no ruler: start from the size on the label of your best-fitting bra and correct it according to how it fits.
| What you notice | Change |
|---|---|
| Band rides up, or you use the tightest hook | Band down one, cup up one |
| Band painful on the loosest hook, cups fine | Band up one, cup down one |
| Spilling over the cups | Cup up one, same band |
| Cups loose or wrinkled all over | Cup down one, same band |
This approach has its own guide, with more detail on each check: find your bra size without measuring.
Things that do not work well
- Guessing from dress size. Dress size says nothing about the gap between your ribcage and your bust, which is what cup size measures.
- Hand spans. Too imprecise. A hand span varies by several centimetres depending on how far you stretch.
- A belt. Usable for the underbust if it is not elasticated, but too stiff and wide to sit properly around the bust.
Getting it right with any method
The rules are the same as with a tape. Keep the string level at the back, snug under the bust and loose over it, and take each measurement twice. A soft tape measure costs very little and is worth picking up for next time. The full technique is in how to measure your bra size.
Frequently asked questions
Can I use a metal tape measure?
Not directly. A steel tape will not follow the curve of your body and will read short. Use it flat on a table to measure a piece of string that you have wrapped around yourself.
Are phone measuring apps accurate enough?
Apps that estimate from photos vary a lot in accuracy, and an error of two or three centimetres is a whole cup size. A length of string and a ruler is more dependable. If you use an app, treat its result as rough and confirm it by trying bras on.
How accurate is the string method?
As accurate as a tape measure, provided the string does not stretch and you mark it carefully. Elastic, wool and stretchy ribbon will give readings that are too small.
Not measured recently? It takes two minutes.
Open the bra size calculator →