How to Read a Glasses Prescription in the UK (2025 Guide)
Confused by SPH, CYL or PD? Don’t worry. This step-by-step guide explains your UK glasses prescription in plain English — with examples and tips before you order online.
Understand your prescription ↓Why prescriptions look complicated (but aren’t)
Eye test results can feel like secret code. Lines of numbers, plus and minus signs, abbreviations like SPH or CYL… no wonder many people feel stuck when they want to order glasses online. But here’s the secret: your prescription follows a standard UK format, and each field has a simple meaning.
Think of it like a recipe: the numbers are just ingredients for your lenses. Once you know what each one means, you can confidently choose frames — and often save £100+ by shopping online for cheap prescription glasses.
✅ You own your prescription
UK law says the optician must give it to you after an eye test. It’s your data — keep it handy.
✅ Same quality lenses
Budget and designer glasses use the same optical standards. What changes is the brand, frame material, and price.
✅ Regular updates
Adults usually test every 2 years. Kids and older adults may need yearly checks.
What your UK glasses prescription actually means
Here are the fields you’ll see on most prescriptions, what they stand for, and what the numbers look like in practice:
| Field | In plain English | Typical range | Example |
|---|---|---|---|
| SPH (Sphere) | Overall power. Minus (−) = short-sighted, Plus (+) = long-sighted. | −10.00 to +8.00 | −2.00 |
| CYL (Cylinder) | Astigmatism strength (irregular eye shape correction). | 0.00 to ±4.00 | −0.75 |
| AXIS | Direction of astigmatism, in degrees. | 1°–180° | 090° |
| ADD | Extra boost for reading (bifocal/varifocal). | +0.75 to +3.00 | +2.00 |
| PD | Pupillary Distance — distance between your pupils. Ensures lenses line up with your eyes. | 54–74 mm | 63 mm |
Signs matter
+ and − are not optional. A plus sign flips the correction completely.
Plano / DS
Means no correction needed. If you see PL or DS, leave that box blank when ordering.
PD: single vs monocular
Some opticians write one number (63 mm). Others split it (31/32 mm). Both work — it just affects lens centring.
How to read your prescription step by step
Once you know what the fields mean, reading your prescription is straightforward. Here’s a five-step process to make sense of any UK prescription:
1. Start with SPH
This shows if you’re short-sighted (−) or long-sighted (+). Higher numbers = stronger correction.
2. Check CYL & AXIS
If you have astigmatism, CYL is the strength, AXIS is the angle. If blank, you don’t need it.
3. Look at ADD
ADD is extra power for reading/varifocals. If you only need distance glasses, this stays empty.
4. Find your PD
Pupillary Distance ensures lenses align with your pupils (single number or left/right split).
5. Double-check the signs
Mixing up + and − is the #1 ordering mistake. Triple-check before checkout.
Affordable frames you can buy online today
Now that you understand your prescription, you can confidently shop online. Here are six stylish, budget-friendly frames from LowCostGlasses — all with lenses included:
Frequently asked questions
What prescription requires glasses for driving in the UK?
UK law requires you to read a number plate from 20 metres away. This typically means vision of 6/12 (Snellen) or better. If your prescription is around −0.75D or higher (short-sight), you’ll likely need glasses to legally drive. Always confirm with your optician.
Can I use my UK prescription to buy glasses online?
Yes — as long as it’s in date (usually within 2 years). Online opticians like LowCostGlasses follow the same standards as high-street opticians, but with lower overheads. Just enter the numbers exactly as written and double-check the +/− signs.
What if my prescription doesn’t list PD?
PD (Pupillary Distance) isn’t always provided. You can ask your optician, or measure it yourself using an online ruler or phone app. Accuracy within 1–2 mm is usually fine for single-vision glasses. For varifocals, a professional measurement is best.
Are cheap prescription glasses any good?
Yes. All lenses sold in the UK must meet British/European safety and optical standards. The difference in price is mostly frame material, brand, and extras like coatings. Cheap glasses are a smart way to have a spare pair or experiment with style.
Ready to order your next pair?
Now that you know exactly how to read your prescription, you can shop online with confidence — and save money at the same time.
Shop Cheap Prescription Glasses at LowCostGlasses →