Greenhouse & Growing Calculators

A greenhouse transforms what you can grow in the UK, extending the season by two months or more at each end. The most popular sizes for UK gardens are 6x8ft (1.8x2.4m) and 8x10ft (2.4x3m), fitting neatly into typical suburban plots. Our greenhouse size calculator helps you choose the right dimensions based on what you plan to grow, while the greenhouse heating calculator works out the wattage needed to keep temperatures above freezing through British winters — critical for overwintering tender plants and getting early tomato and pepper seedlings going in February and March.

Polytunnels offer a cost-effective alternative and are increasingly popular on UK allotments, with standard widths of 3m, 4.2m, and 4.8m. The polytunnel calculator helps you work out the polythene cover needed, accounting for burial at the edges. Ventilation is essential in any growing structure — UK summers can push greenhouse temperatures above 40 degrees Celsius on sunny days. Our ventilation calculator ensures you have enough roof vents and louvre windows, following the general rule that vent area should equal at least 20% of floor area.

For gardeners without a greenhouse, cold frames, cloches, and horticultural fleece all help protect plants from late frosts, which can occur in much of England until mid-May and even later in Scotland. The fleece coverage calculator works out how much frost protection fabric you need, while the seed starting calculator accounts for germination rates so you sow enough seeds to achieve your target number of healthy transplants. The propagation calculator helps plan heated propagator use for warmth-loving crops like aubergines and chillies.