You don't need a jeweller or any special tools to find your size. Everything you need is probably already in a drawer at home. You'll need:

• A thin strip of paper or a piece of non-stretchy string
• A ruler or measuring tape (in millimetres)
• A pen

Cut the paper to about 1 cm wide and 10 cm long. Paper tends to give a more accurate result than string, which can stretch or twist as you wrap it and throw your measurement out by a size.

Wrap the paper around the base of the finger you'll wear the ring on. For an engagement ring, that's traditionally the fourth finger of your left hand. The paper should sit snugly without pinching. If you can slide it over your knuckle with a bit of resistance, that's about right.

Keep the strip flat and level as you wrap it. If it angles up your finger or bunches at the back, it will read larger than your true size.

Holding the paper in place, use your pen to mark the spot where it meets itself. That length is the circumference of your finger.

Be as precise as you can here. A millimetre or so can be the difference between one ring size and the next, so a fine-tipped pen and a steady hand go a long way. It can help to ask someone to make the mark for you while you hold the paper still.

Lay the paper flat and measure from the end to your mark in millimetres. Then find that measurement on our ring size chart. If you land between two sizes, go with the larger one.

Jot your measurement down somewhere safe once you have it. It's useful to keep for later, so if you're ever adding a wedding band or a second ring down the track, you won't need to measure again.

Email us at hello@unadiamond.com with your measurement and the ring you're looking at, and we'll help you choose. Wider bands usually need a slightly larger size than slim ones, and we can factor that in.

If your ring doesn't fit quite right once it arrives, get in touch and we'll talk you through resizing. Rings with diamonds set all the way around the band are much harder to resize, so it's worth measuring twice for those.

Because every Una ring is made to order, a quick question before you check out is always easier than a resize afterwards. Never feel like you're bothering us. Helping you get the fit right is part of what we do.

• Measure at the end of the day, when your fingers are at their largest.
• Avoid measuring when your hands are cold, as fingers shrink a little.
• Measure two or three times to make sure you get the same result.
• If your knuckle is bigger than the base of your finger, measure both and choose a size in between so the ring slides on but won't spin.

• Borrow a ring they already wear on the right finger, then measure the inside diameter in millimetres or trace the inside of it on paper.
• Press the ring into a bar of soap to keep an impression you can measure later.
• Ask a close friend or family member. They might already know, or be able to find out without giving the game away.
• If all else fails, email us. We can help you make a sensible guess and talk you through resizing if it's needed.