To cover tomatoes for frost, you need fabric wide enough to go over the plants or hoops and reach the ground on both sides, plus about a foot each side to pin down. Choose a lightweight cover for about 2°F of protection or a heavyweight one for up to 8°F. Enter your bed size and forecast below for the fabric size, weight, and hoops to buy.
Try a preset:
Your entries stay in your browser. Nothing is sent to a server or saved to an account.
What Your Result Means: the fabric size is the smallest piece that covers the bed and reaches the ground all round with about a foot to anchor. Buy the next size up. The fabric weight is matched to your forecast low, using the same temperature bands as our Frost Protection Checker.
How Much Frost Cloth Do You Need for Tomatoes?
Measure the bed, decide whether the cover will float on the plants or sit on hoops, and check the forecast low. The cover has to reach the soil on every side, because frost protection comes from heat held in by the ground.
- Measure the bed length and width in feet.
- Choose hoops or floating, and enter the hoop height or the plant height.
- Enter the forecast low to get the right fabric weight.
- Cover before sunset, pin the edges, and uncover on sunny mornings.
Frost Cloth Weight Chart
| Cover Weight | Frost Protection | Light Through | Use For Tomatoes |
|---|---|---|---|
| Light (0.45 oz/sq yd) | About 2°F | 90 to 95% | Cool nights, 40 to 45°F |
| Medium (0.5 to 1.0 oz) | 4 to 6°F | 70 to 85% | Chilly nights, 33 to 39°F |
| Heavy (1.5 to 2.2 oz) | Up to 8°F | 30 to 50% | Light frost, 29 to 32°F; remove by day |
How Does the Frost Cloth Calculator Work?
Fabric width = over the top + 2 ft (1 ft each side to anchor)
Fabric length = bed length + 2 x height + 2 ft
Hoops = bed length / 3 ft, rounded up, + 1; each hoop about bed width + 2 x height
Weight: 40 to 45°F light; 33 to 39°F medium; 29 to 32°F heavy; 28°F or below harvest
The width-plus-twice-the-height rule matches University of Maryland Extension’s example of a 7-foot wire forming a hoop 3 feet wide and 2 feet tall. The 1-foot anchoring allowance is our practical estimate.
Worked Example
Say you have an 8 by 4 foot bed with 2-foot hoops and a forecast low of 36°F. Over the top is 4 + 2 x 2 = 8 feet, so the fabric needs to be 10 feet wide and 8 + 4 + 2 = 14 feet long. You need 4 hoops, each about 8 feet of wire, and a medium-weight cover for 4 to 6°F of protection.
Factors That Change the Result
- Wind: windy nights pull heat away; anchor edges well and add a heavier cover.
- Clear skies: calm, clear nights are the frostiest.
- Contact: leaves touching the fabric can still be nipped; hoops help.
- Soil moisture: moist soil holds and releases more heat overnight than dry soil.
- Plant size: tall fall plants need taller hoops or stakes and a bigger cover.
Common Mistakes to Avoid
- Cover too narrow: gaps at the soil let cold air in and warm air out.
- Leaving heavy covers on all day: they block much of the light.
- Plastic on the leaves: it offers little frost protection and scorches in sun.
- Covering too late: put covers on before sunset to trap the day’s heat.
- Trusting covers in a hard freeze: at 28°F or below, harvest the fruit.
Accuracy and Limitations
These are practical estimates.
What It Does Well: sizes fabric and hoops and matches cover weight to the forecast.
What It Does Not Do: guarantee protection. Actual results depend on wind, sky, and how well edges are sealed. This is general guidance, not professional advice.
Methodology
Method: fabric width and length from bed size plus twice the hoop or plant height, plus a 1-foot anchoring allowance each side (our estimate). Fabric weights and protection: light 0.45 oz/sq yd, about 2°F, 90 to 95% light; medium 0.5 to 1.0 oz, 4 to 6°F, 70 to 85% light; heavy 1.5 to 2.2 oz, up to 8°F, 30 to 50% light (University of Maryland Extension). Hoops: 7-foot wire makes a 3-foot wide, 2-foot tall arch; low tunnels 15 to 30 inches high with hoops 2 to 4 feet apart (Maryland); we use 3 feet. Tomatoes: flowers may drop above 90°F under covers (Maryland). Temperature bands: match our Frost Protection Checker. Anchoring: pins, boards, bricks, sandbags, rocks, or soil (Maryland; University of New Hampshire).
Sources: University of Maryland Extension – Row Covers, UNH Extension – Using Row Covers in the Garden. Last reviewed: September 28, 2026 · Reviewed by Aiza Anwar.
Frequently Asked Questions
How much frost protection does a row cover give?
About 2°F for lightweight covers (0.45 oz per square yard), 4 to 6°F for medium weights (0.5 to 1.0 oz), and up to 8°F for heavyweight covers (1.5 to 2.2 oz), according to University of Maryland Extension.
How big should frost cloth be for a tomato bed?
Wide enough to go over the plants or hoops and reach the ground on both sides with extra to pin down. For hoops, the cloth width is roughly the bed width plus twice the hoop height, plus about a foot each side to anchor.
Do I need hoops for frost cloth on tomatoes?
Hoops are recommended for medium and heavy covers and keep fabric off the leaves, where frost can still damage the contact points. Light covers can float directly on the plants with some slack.
How far apart should row cover hoops be?
About 2 to 4 feet apart for low tunnels 15 to 30 inches high, per University of Maryland Extension. A 7-foot wire makes a hoop about 3 feet wide and 2 feet tall.
Can I leave frost cloth on tomatoes during the day?
Light covers can stay on in cool weather, but heavy covers block 50 to 70% of the light, so take them off on sunny days. Under covers in summer, tomato flowers can drop when days top 90°F.
Will frost cloth save tomatoes in a hard freeze?
Not reliably. Covers add a few degrees; below about 28°F, pick all mature green and colored fruit instead.
How do I hold frost cloth down?
Pin the edges with sod pins or landscape staples, or weigh them down with boards, bricks, sandbags, rocks, or soil so wind cannot lift them.
Can I use a bedsheet instead of frost cloth?
An old sheet or blanket over stakes can help for a night, but remove it in the morning and do not let plastic touch the leaves.
Related Tomato Tools
See Tomato Problems & Solutions
This calculator gives general sizing and cover guidance, not a guarantee of frost protection. Watch the forecast and harvest ripening fruit before a hard freeze. Spotted an error? Tell us here.