This contact lens vertex conversion chart compares glasses and contact lens optical powers at a 12 mm spectacle vertex distance. It is spherical-only: CYL = 0. Read the forward and reverse tables separately so that the input and output planes are clear.
Each direction covers −12.00 to +12.00 D in 0.25 D input steps. Raw powers and 0.25 D display values are separate. This is an educational reference; it does not determine a fitted prescription or select an available lens product.
Glasses to Contacts Conversion Chart — 12 mm
Read from glasses SPH to theoretical contact-plane power. Use Fc = Fs / (1 − d × Fs), with d = 0.012 m. Minus powers become less negative; plus powers become more positive.
| Glasses SPH (D) | Raw contact power (D) | 0.25 D display |
|---|---|---|
| -12.00 | -10.4895 | -10.50 |
| -11.75 | -10.2980 | -10.25 |
| -11.50 | -10.1054 | -10.00 |
| -11.25 | -9.9119 | -10.00 |
| -11.00 | -9.7173 | -9.75 |
| -10.75 | -9.5217 | -9.50 |
| -10.50 | -9.3250 | -9.25 |
| -10.25 | -9.1273 | -9.25 |
| -10.00 | -8.9286 | -9.00 |
| -9.75 | -8.7287 | -8.75 |
| -9.50 | -8.5278 | -8.50 |
| -9.25 | -8.3258 | -8.25 |
| -9.00 | -8.1227 | -8.00 |
| -8.75 | -7.9186 | -8.00 |
| -8.50 | -7.7132 | -7.75 |
| -8.25 | -7.5068 | -7.50 |
| -8.00 | -7.2993 | -7.25 |
| -7.75 | -7.0906 | -7.00 |
| -7.50 | -6.8807 | -7.00 |
| -7.25 | -6.6697 | -6.75 |
| -7.00 | -6.4576 | -6.50 |
| -6.75 | -6.2442 | -6.25 |
| -6.50 | -6.0297 | -6.00 |
| -6.25 | -5.8140 | -5.75 |
| -6.00 | -5.5970 | -5.50 |
| -5.75 | -5.3789 | -5.50 |
| -5.50 | -5.1595 | -5.25 |
| -5.25 | -4.9389 | -5.00 |
| -5.00 | -4.7170 | -4.75 |
| -4.75 | -4.4939 | -4.50 |
| -4.50 | -4.2694 | -4.25 |
| -4.25 | -4.0438 | -4.00 |
| -4.00 | -3.8168 | -3.75 |
| -3.75 | -3.5885 | -3.50 |
| -3.50 | -3.3589 | -3.25 |
| -3.25 | -3.1280 | -3.25 |
| -3.00 | -2.8958 | -3.00 |
| -2.75 | -2.6621 | -2.75 |
| -2.50 | -2.4272 | -2.50 |
| -2.25 | -2.1908 | -2.25 |
| -2.00 | -1.9531 | -2.00 |
| -1.75 | -1.7140 | -1.75 |
| -1.50 | -1.4735 | -1.50 |
| -1.25 | -1.2315 | -1.25 |
| -1.00 | -0.9881 | -1.00 |
| -0.75 | -0.7433 | -0.75 |
| -0.50 | -0.4970 | -0.50 |
| -0.25 | -0.2493 | -0.25 |
| 0.00 | 0.0000 | 0.00 |
| Glasses SPH (D) | Raw contact power (D) | 0.25 D display |
|---|---|---|
| +0.25 | +0.2508 | +0.25 |
| +0.50 | +0.5030 | +0.50 |
| +0.75 | +0.7568 | +0.75 |
| +1.00 | +1.0121 | +1.00 |
| +1.25 | +1.2690 | +1.25 |
| +1.50 | +1.5275 | +1.50 |
| +1.75 | +1.7875 | +1.75 |
| +2.00 | +2.0492 | +2.00 |
| +2.25 | +2.3124 | +2.25 |
| +2.50 | +2.5773 | +2.50 |
| +2.75 | +2.8438 | +2.75 |
| +3.00 | +3.1120 | +3.00 |
| +3.25 | +3.3819 | +3.50 |
| +3.50 | +3.6534 | +3.75 |
| +3.75 | +3.9267 | +4.00 |
| +4.00 | +4.2017 | +4.25 |
| +4.25 | +4.4784 | +4.50 |
| +4.50 | +4.7569 | +4.75 |
| +4.75 | +5.0371 | +5.00 |
| +5.00 | +5.3191 | +5.25 |
| +5.25 | +5.6030 | +5.50 |
| +5.50 | +5.8887 | +6.00 |
| +5.75 | +6.1762 | +6.25 |
| +6.00 | +6.4655 | +6.50 |
| +6.25 | +6.7568 | +6.75 |
| +6.50 | +7.0499 | +7.00 |
| +6.75 | +7.3449 | +7.25 |
| +7.00 | +7.6419 | +7.75 |
| +7.25 | +7.9409 | +8.00 |
| +7.50 | +8.2418 | +8.25 |
| +7.75 | +8.5447 | +8.50 |
| +8.00 | +8.8496 | +8.75 |
| +8.25 | +9.1565 | +9.25 |
| +8.50 | +9.4655 | +9.50 |
| +8.75 | +9.7765 | +9.75 |
| +9.00 | +10.0897 | +10.00 |
| +9.25 | +10.4049 | +10.50 |
| +9.50 | +10.7223 | +10.75 |
| +9.75 | +11.0419 | +11.00 |
| +10.00 | +11.3636 | +11.25 |
| +10.25 | +11.6876 | +11.75 |
| +10.50 | +12.0137 | +12.00 |
| +10.75 | +12.3421 | +12.25 |
| +11.00 | +12.6728 | +12.75 |
| +11.25 | +13.0058 | +13.00 |
| +11.50 | +13.3411 | +13.25 |
| +11.75 | +13.6787 | +13.75 |
| +12.00 | +14.0187 | +14.00 |
Contacts to Glasses Conversion Chart — 12 mm
Read from contact SPH to theoretical spectacle-plane power. The algebraic inverse is Fs = Fc / (1 + d × Fc). Minus contact powers become more negative; plus contact powers become less positive.
| Contact SPH (D) | Raw glasses power (D) | 0.25 D display |
|---|---|---|
| -12.00 | -14.0187 | -14.00 |
| -11.75 | -13.6787 | -13.75 |
| -11.50 | -13.3411 | -13.25 |
| -11.25 | -13.0058 | -13.00 |
| -11.00 | -12.6728 | -12.75 |
| -10.75 | -12.3421 | -12.25 |
| -10.50 | -12.0137 | -12.00 |
| -10.25 | -11.6876 | -11.75 |
| -10.00 | -11.3636 | -11.25 |
| -9.75 | -11.0419 | -11.00 |
| -9.50 | -10.7223 | -10.75 |
| -9.25 | -10.4049 | -10.50 |
| -9.00 | -10.0897 | -10.00 |
| -8.75 | -9.7765 | -9.75 |
| -8.50 | -9.4655 | -9.50 |
| -8.25 | -9.1565 | -9.25 |
| -8.00 | -8.8496 | -8.75 |
| -7.75 | -8.5447 | -8.50 |
| -7.50 | -8.2418 | -8.25 |
| -7.25 | -7.9409 | -8.00 |
| -7.00 | -7.6419 | -7.75 |
| -6.75 | -7.3449 | -7.25 |
| -6.50 | -7.0499 | -7.00 |
| -6.25 | -6.7568 | -6.75 |
| -6.00 | -6.4655 | -6.50 |
| -5.75 | -6.1762 | -6.25 |
| -5.50 | -5.8887 | -6.00 |
| -5.25 | -5.6030 | -5.50 |
| -5.00 | -5.3191 | -5.25 |
| -4.75 | -5.0371 | -5.00 |
| -4.50 | -4.7569 | -4.75 |
| -4.25 | -4.4784 | -4.50 |
| -4.00 | -4.2017 | -4.25 |
| -3.75 | -3.9267 | -4.00 |
| -3.50 | -3.6534 | -3.75 |
| -3.25 | -3.3819 | -3.50 |
| -3.00 | -3.1120 | -3.00 |
| -2.75 | -2.8438 | -2.75 |
| -2.50 | -2.5773 | -2.50 |
| -2.25 | -2.3124 | -2.25 |
| -2.00 | -2.0492 | -2.00 |
| -1.75 | -1.7875 | -1.75 |
| -1.50 | -1.5275 | -1.50 |
| -1.25 | -1.2690 | -1.25 |
| -1.00 | -1.0121 | -1.00 |
| -0.75 | -0.7568 | -0.75 |
| -0.50 | -0.5030 | -0.50 |
| -0.25 | -0.2508 | -0.25 |
| 0.00 | 0.0000 | 0.00 |
| Contact SPH (D) | Raw glasses power (D) | 0.25 D display |
|---|---|---|
| +0.25 | +0.2493 | +0.25 |
| +0.50 | +0.4970 | +0.50 |
| +0.75 | +0.7433 | +0.75 |
| +1.00 | +0.9881 | +1.00 |
| +1.25 | +1.2315 | +1.25 |
| +1.50 | +1.4735 | +1.50 |
| +1.75 | +1.7140 | +1.75 |
| +2.00 | +1.9531 | +2.00 |
| +2.25 | +2.1908 | +2.25 |
| +2.50 | +2.4272 | +2.50 |
| +2.75 | +2.6621 | +2.75 |
| +3.00 | +2.8958 | +3.00 |
| +3.25 | +3.1280 | +3.25 |
| +3.50 | +3.3589 | +3.25 |
| +3.75 | +3.5885 | +3.50 |
| +4.00 | +3.8168 | +3.75 |
| +4.25 | +4.0438 | +4.00 |
| +4.50 | +4.2694 | +4.25 |
| +4.75 | +4.4939 | +4.50 |
| +5.00 | +4.7170 | +4.75 |
| +5.25 | +4.9389 | +5.00 |
| +5.50 | +5.1595 | +5.25 |
| +5.75 | +5.3789 | +5.50 |
| +6.00 | +5.5970 | +5.50 |
| +6.25 | +5.8140 | +5.75 |
| +6.50 | +6.0297 | +6.00 |
| +6.75 | +6.2442 | +6.25 |
| +7.00 | +6.4576 | +6.50 |
| +7.25 | +6.6697 | +6.75 |
| +7.50 | +6.8807 | +7.00 |
| +7.75 | +7.0906 | +7.00 |
| +8.00 | +7.2993 | +7.25 |
| +8.25 | +7.5068 | +7.50 |
| +8.50 | +7.7132 | +7.75 |
| +8.75 | +7.9186 | +8.00 |
| +9.00 | +8.1227 | +8.00 |
| +9.25 | +8.3258 | +8.25 |
| +9.50 | +8.5278 | +8.50 |
| +9.75 | +8.7287 | +8.75 |
| +10.00 | +8.9286 | +9.00 |
| +10.25 | +9.1273 | +9.25 |
| +10.50 | +9.3250 | +9.25 |
| +10.75 | +9.5217 | +9.50 |
| +11.00 | +9.7173 | +9.75 |
| +11.25 | +9.9119 | +10.00 |
| +11.50 | +10.1054 | +10.00 |
| +11.75 | +10.2980 | +10.25 |
| +12.00 | +10.4895 | +10.50 |
How 10, 12 and 14 mm Change the Result
The tables above assume 12 mm. The examples below show why the distance must be part of the calculation. Each cell shows the raw result followed by its 0.25 D display. These distances are comparison inputs, not a universal fitting recommendation.
| Input SPH | 10 mm | 12 mm | 14 mm |
|---|---|---|---|
| -8.00 | -7.4074-7.50 | -7.2993-7.25 | -7.1942-7.25 |
| -5.50 | -5.2133-5.25 | -5.1595-5.25 | -5.1068-5.00 |
| +4.00 | +4.1667+4.25 | +4.2017+4.25 | +4.2373+4.25 |
| +6.50 | +6.9519+7.00 | +7.0499+7.00 | +7.1507+7.25 |
| Input SPH | 10 mm | 12 mm | 14 mm |
|---|---|---|---|
| -8.00 | -8.6957-8.75 | -8.8496-8.75 | -9.0090-9.00 |
| -5.50 | -5.8201-5.75 | -5.8887-6.00 | -5.9588-6.00 |
| +4.00 | +3.8462+3.75 | +3.8168+3.75 | +3.7879+3.75 |
| +6.50 | +6.1033+6.00 | +6.0297+6.00 | +5.9578+6.00 |
For your own distance and powers, use the two-way vertex distance calculator. Its input range is wider than this compact reference chart.
Why a Spherical Chart Is Not Enough for CYL
These tables assume CYL = 0. For −8.00 / −2.00 × 180°, calculate the meridians S = −8.00 and S + C = −10.00 separately. At 12 mm they give raw powers of -7.2993 D and -8.9286 D. Their difference gives raw CYL -1.6293 D; the display is -7.25 / -1.75 × 180°.
Use the vertex calculator with SPH, CYL and axis when CYL is present. Product powers and on-eye rotation are separate fitting considerations.
Rounding and Prescription Limits
Inputs run from −12.00 to +12.00 D in 0.25 D steps. Raw powers are printed to four decimal places. Display values are rounded to the nearest 0.25 D; exact half steps round away from zero. This is the website's display convention, not a universal product increment or standards certification.
The reverse chart inverts the optical equation, not the prescribing process. Product selection and rounding can lose information, so reversing a rounded value does not necessarily recover the original number. Neither chart determines BC, DIA, ADD, prism, PD, lens brand, current refraction or clinical suitability.
For the difference between the two documents, read contact lens prescriptions versus glasses prescriptions.
Calculation References
ACUVUE Simplifit describes vertex calculation across each power meridian. CooperVision Toric Calculator distinguishes theoretical power from product parameters and professional fitting. The reverse equation here is the algebraic inverse of the forward equation; these references do not imply manufacturer endorsement of VertexLensCalc.
