Rulers to cut out at actual size: 6 inches in halves to sixteenths, 15 centimetres in millimetres, or both on the same ruler.
A cut-out ruler lets every student measure at their own desk. Printed at actual size, it measures the same as a ruler from the shop.
Print at 100% (not fit to page) and check a printed inch against a real ruler. Laminate or print on card so the edges stay straight.