Frame & Mat Size Calculator

Measure and plan

1. Measure the entire sheet, including printed white margins. Enter its width and height.
2. Choose how much of each sheet edge the mat will cover. Check signatures and important marks before choosing overlap.
3. Choose a border to calculate an internal frame size, or enter your frame’s internal insert size to calculate borders.

What the calculator shows

• Calculates the opening, four borders and outside mat size from unrounded measurements.
• Tests whether the full sheet fits, including after a deliberate 90° rotation.
• Compares common metric, ISO and inch reference dimensions with adjusted borders.
• Retains the exact source dimensions of inch and ISO references instead of treating nearby metric labels as equivalent.

When to use it

• Plan a mat for a print with an existing white border.
• Check whether a measured sheet fits a frame you already own.
• Compare an A-series sheet with inch and metric frame references.

Understand the dimensions

A 200 × 300 mm sheet with 3 mm overlap leaves a 194 × 294 mm opening. With 40 mm top and side borders, the outside mat is 274 × 374 mm.

Adding 10 mm only to the bottom makes that mat 274 × 384 mm. Bottom weighting is a visual preference, not a requirement.

An 8 × 10 inch reference is exactly 203.2 × 254 mm; A4 is 210 × 297 mm. Neither is interchangeable with a nearby metric label.

The frame’s internal size describes the insert or backing it accepts. The outside moulding size and visible front opening depend on the frame lip and rebate.

Nominal sizes do not include cutter tolerances, bevels, mounting method or material thickness. Check the actual frame and ask a framer when precise fit or valuable artwork matters.

Privacy and scope

Your measurements stay in this browser calculation. Ordinary site services may still make requests.

This plan covers one rectangular opening. It does not determine a safe mounting method or guarantee stock sizes.