Matboard calculator

With optical centring off, the opening sits in the exact centre: left and right borders match, and top and bottom borders match. All four borders are equal only when the horizontal and vertical space allows it.

Optical centring uses the original WILDFOTO calculator’s adjustment. It moves the opening upwards by the side border divided by the outer mat width, multiplied by the centred top border. The bottom grows by the same amount that the top shrinks.

Enter the finished opening size, allowing for how much of the print you want hidden behind the mat. Measurements run from the outer mat edge to the opening. Frame moulding, bevel allowances and cutting-machine offsets are not included. Results are rounded to three decimal places; check your measurements before cutting.